Faraday's Gold

In 1856, Michael Faraday (1791-1867) carried out a series of researches on the "colors of gold." The results were published as "Experimental relations of gold (and other metals) to light," in the Philosophical Transactions in 1857 and reprinted in his 1859 book Experimental Researches in Chemistry and Physics, pp. 391-442 (London: Richard Taylor & William Francis). His laboratory diary covering this work was transcribed and published by Thomas Martin in 1936 as volume 7 of Faraday's Diary (London: G. Bell).

In 1998, I noticed a series of microscope slides made by Faraday as part of this research, held in the museum area of the Royal Institution of Great Britain. Over the next several years, I photographed all of the surviving slides (and a number of other relevant specimens), and this web page contains the results. The specimens are an integral part of the Diary, which becomes a vivid document of Faraday's research, when viewed along with a reading of the Diary.

Each specimen is shown below, together with commentary (by Faraday, in bold font, and by me in regular font). Clicking on any thumbnail will open a large image in a separate window. These can be studied closely, to reveal details seen by Faraday.

Further information: R.D. Tweney (2006). Discovering discovery: How Faraday found the first metallic colloid. Perspectives on Science, 14(1), 97-121 [Download PDF].

Contact Information: Email Ryan Tweney

Please note: The material in this website is copyrighted and is for individual use only. Distribution of any sort requires permission.

Michael Faraday's Comments (from his Diary) are shown in bold italic type.

Ryan Tweney's comments are shown in regular type. CLICK IMAGES FOR LARGER VIEW

The first image shows some gold colloids prepared by Faraday (ambient light). The second image shows the "Faraday-Tyndall Effect." The specimen on the right in the second image is not a colloid.

A large (3") gold leaf mounted by Faraday for lecture-demonstrations. Note the green color (left) of light passed through the leaf.

Box 1-99

1 to 42, films of gold, 14671, 6.

Faraday's comment (in bold italic) "1 to 42" refers to slide numbers. "14671,6" refers to Diary entries 14671 and 14676.

1 to 23, increasing in thickness, 14671, 6

The first image was taken in ambient light and the second in transmitted light. Note the difference in background color.

The third image was taken at greater magnification (about 1x) compared to the first two (less than 1/3x). Note the increased detail.

No. 3 was changed to No. 35; some overscribing is visible on 35.

No. 4 broken into 2 pieces, 5 Feby. - by a fall.

See entry 14390, 11 February 1856

Note that this slide, like many others, shows the results of Faraday's "scribing" of the surface.

8, 11, 12, 15, graduated or sliding thicknesses, 15238

Note the chip at the right edge of the slide.

No. 10 was changed to No. 95.

No. 13 is broken.

A central area has been scraped clear on this slide.

very dark made 96

No. 17 changed to No. 96; "made 96" is crossed out.

Note that the films from here to No. 21 are quite thick.

See entry 14429, 15 February 1856. Faraday tried unsuccessfully to produce green by pressure.

beaten gold leaf

has been heated

No. 27 is broken; the two halves are present.

in Canada balsam

No. 28 is the only slide with a cover slip.

29-33 on polished card

on dull unpolished card

5-39, two films superposed, 14671.

No. 35 changed from No. 3.

Note that the second image is in reflected light.

40, 41, three films superposed, 14625

Four films superposed, 14625.

43-46. Palladium, 14622, 72, 5239

47-49. Silver, 14672

silvered tube in halves

These are the halves of a broken test tube silvered on the inside. They were kept in the long box, "Day's Cubas."

Thirteen superposed films of Gold, 14625

Film, Silver from Nitrate by phosphorus vapour.

No. 52 scribed; "silver reduced from AgO NO2 with vapor of oil of cloves"

Film, Silver from Ammoniacal Solution by phosphorus vapour

Gold precipitated by Su. Iron (14353), 14640, 70.

55, 56, 57, 58, 58b. Thick gold films by phosphorus (14352, 4, 8), 14671.

This film is opaque; a bit of reflected light was used to show surface texture.

58b

Silver by Electy. on zinc, N.A., etc. (14375).

No. 59 is in the long box, "Day's Cubas." A glass fragment about 2" on a side.

Do. . . . . . . . . . (14375)

This and No. 59 are the first slides referred to by number in the Diary, on 11 February 1856.

Gold Do. . . . . . . . . (14381)

No. 61 in long box, "Day's Cubas"

Do. . . . . . . . . . (14384)

No. 62 in long box, "Day's Cubas"

Do. . . . . . . on paper (14385)

Do. . . . . . . on glass (14386)

No. 64 in long box, "Day's Cubas"

Do. . on one side . Do. (14415), 621, 72

Do. . two films . Do. (14416), 621

Deep gold on sol. chlorine - residue (14420)

"Deep gold" is a type of commercial gold leaf. See entry 14423 where Faraday defines the types.

68-73. Do. progressive. . (14420), 14628, 69, 5237.

Nos. 68-73 were thinned by floating them on solution of chlorine. No. 68 is the thickest. See entry 14420.

74-82. Extra deep gold. Do. . . (14421), 14620, 69.

"Extra deep gold" is a type of commercial gold leaf. See entry 14423. Nos. 74-82 were thinned by solution of chlorine.

This slide has a folded or "crinkled" area.

This slide and No. 84 were thinned by Muriatic Acid (HCl). See entry 14431.

De la Rue's film of Platinum . . 14622.

The deposit on this slide is very thin. It can barely be seen in this underexposure but is more visible when viewed edge-on.

86-92. High gold subjected to different fluids (14441).

No. 86 from "water" (see entry 14441).

No. 87 from "strong Sul. acid" (see entry 14441).

No. 88 from "strong Nitric acid" (see entry 14441).

No. 89 "dil. N.M. acid" i.e., dilute Nitro Muriatic acid, or Aqua Regia. (see entry 14441).

No. 90 from "over caustic potassa" (see entry 14441).

No. 91 from "ammonia" (see entry 14441).

No. 92 from "Bichromate potassa" (see entry 14441).

Leaf Gold heated (14486), 624, 745.

No. 93 broken; 2 pieces. Examined by Faraday at De La Rue's, 200x, 23 May 1856. See entry 14745.

White Gold heated (14487), 624, 73.

No. 94 inscribed "1/12 550." See entry 17745. Note that the slide is warped from heating.

Purple gold film heated (14488) - also pressed (14529), 14566, 626, 74.

No. 95 changed from No. 10. Examined at 50x and 700x. See entry 14750.

Phosphorus Gold film, 17, heated by blow pipe (14494, 566, 626, 74, 6).

No. 96 warped; changed from No. 17.

Extra deep gold leaf - heated between glass (14496, 624) and pressed (14531, 14673).

White Gold leaf heated between glass (14487, 624).

Silver leaf heated between glass (14498).

Note that the base slide is broken and that a glass fragment is cemented over part of the silver leaf.

Note also, in this box, item "97" which may be a cover for another slide. It is not slide No. 97.

Box 100-120; 386-405

This box contains a discontinuous sequence. See below for slides 386-405.

100

No. 100; nothing visible; film non-adhering?

101

(14531) - Phos. Gold film - weak solution.

Note the extensive wrinkling of the film.

102

103

- 14567 - are as No. 180.

103 renumbered as 194

104

- 14567 - Do.

No. 104 renumbered as 195

105

- (14532) - Phos. gold film - stronger solution. Good - thin and regular.

No. 105 renumbered as 232

106

No. 106 renumbered as 180

107

No. 107 renumbered as 233

108

-14671.

109

-14567.

No. 109 renumbered as 196

110

(14533) - Phos. gold film - strong solution, long time.

No. 110 renumbered as 181

111

No. 111 (14536) - salt and N.A.; no action on the film.

112

Renumbered as 182 (14537)

113

Renumbered as 183 (14537)

114

115

- 14647

See entry 14647.

116

- (14534) - Phos. gold film - strong solution - strong phosphorus - in dark.

117

118

14671

119

120

Box 121-215

121 to 129. Parts of the same leaf of deep gold - 121 not altered at all, 122 to 129 (14620) thinned by sol. cyanide of potassium (14669) more or less (14499).

121

122

123

124

Observed by Faraday at 50x and 700x 14743, 23 May 1856. See entry 14743.

125

126

127

128

129

130 to 139. Parts of the same leaf of silver - 130 not altered but the rest thinned by sol. cyanide of potassium (14500, 14669).

130

131

132

133

134

135

See 14744; observed by Faraday at 700x; No. 135 is peeling from the glass.

136

137

138

139

140 to 148. Parts of the same leaf of copper: 140 not altered - the rest thinned by surface contact with solution cyanide potassm. 141 on the cyanide and off again directly (14505, 623, 69).

140

141

142

143

144

145

146

147

148

149-155. Copper films immersed in the old solution of cyanide (14507).

149

150

151

152

153

154

155

156-164. Dutch metal in and on the sol. cyanide (14510).

156

"Dutch gold" is a brass-like alloy containing more copper than brass.

157

158

159

160

161

162

163

Note that this specimen seems out of series, being much thicker than the others. See entry 14510.

164

165

Silver film off nitric acid good (14511). Also No. 166 (14623).

166

167

Silver from under cyanide potassm. (14519).

168

Silver from under cyanide potassm. and salt (14523).

169-173. Silvers on solution of chlorine. (14524, 14669).

169

170

Much overexposed to show detail.

171

172

173

174-179. Gold and silver on glass - heated (14537, 623, 73).

174

highly heated

No. 174 is warped

175

176

177

178

broke in heating

179

No. 179 is warped.

180-183. Phos. gold films - heated (14537-43, 14563, 4, 5, 626, 74, 6).

180

Fine film heated, 14563, 5, 14532, 626, 74 - becomes green by pressure.

This slide was No. 106. The green areas are very subtle and may not be evident in the images. Look for them in the upper part of the transmitted light images.

181

This slide was No. 110. Note the reflected light image, which shows the folding very well.

182

This slide was No. 112. Note the broken corner.

183

This slide was No. 113.

184-193. Gold and silver leaf on glass - heated, 14624, 73.

184

No. 184 is broken.

185

186

Marked "IIc"

187

Marked "IIa"

188

Marked "IIIc"

189

No. 189 broken; 2 pieces (second piece not shown).

190

This slide is warped, as shown. Note that the dim number "190" appears clearly in the edge-on image.

191

Marked "IVd"

192

Marked "Vc"

193

Marked "VIc"

194

Gold film heated, burnishes green, 14567, 674, 6.

Was 103; Faraday says "109" in entry 14567. The green is evident in the last image.

195

Do. . . . . Do. . . 14568, 674, 6.

No. 195 is broken. This slide was No. 104.

196

Do. . . . . Do. . . 14567, 9, 674, 6.

This slide was No. 109.

197

Gold film, phos., 14570, 7, 87, 625.

No. 197 is broken.

198

Do. . . . . . . . . . .

199

Do. . . . . . . . . . . heated, 14578, 87, 97, 626.

No. 199 is chipped.

200

Do. . . . . . . . . . . heated, 14578, 87, 97, 674, 6.

201

Do. . . . . 14571, 7, 88.

202

Do. . . . . . . . . . . heated, 14578, 88, 676.

203

Do. . . . . . . . . . . heated, 14578, 88, 97, 674.

204

Do. . . . . . . . . . .

205

Do. . . . . 14572, 7.

206

Do. . . . . 14572, 7.

207

Do. . . . . . . . . . .

208

Do. . . . . . . . . . . heated, 14578, 89, 674, 6.

209

Do. . . . . . . . . . . heated, 14578, 89.

210

Do. . . . . . . . . . .

211

Do. . . . . 14573, 7, . . . heated, 14578, 90, 676.

212

Do. . . . . . . . . . . heated, 14578, 90, 9.

No. 212 is broken.

213

'Do. . . . . . . . . . .

214

Do. . . . . 14573, 7, 90

215

Do. . . . . . . . . . .

Box 216-305

216

Do. . . . . . . . . . .

217

Do. . . . . . . . . . . heated, 14578, 90, 626.

218

Deposit from XXXI, ruby fluid, on glass, 14579, 600, 36.

This is the first of a series of dried colloids.

219

Do. . . . . . . . . . . . . 14579, heated, 14600, 36.

220

Do. . . . . . . . . . . . . 14579, 600, 3, 27, 36.

221

Do. . . . . . . . . . . . . 14579, heated, 14600.

222

Do. . . . XXIII, violet fluid . . . 14579, 601, 36.

223

Do. . . . XXIII . . . . . . . 14579, heated, 14600.

224

Deposit from XLV, ruby by salt, on glass, 14591, 605, 37.

225

Do. . . . . . . . . . . . . 14591, 605.

226

Do. . . . . . . . . . . . . 14591, 605.

227

Do. . . . . . . . . . . heated 14591, 605, 37.

228

Do. . . . finer state . . . . . . 14592, 606, 37.

229

Deposit from XXXI, on glass, 14595, 604, 36.

230

Do. . . . . . . . . 14595, 604.

No. 230 is broken.

231

Do. . . . . . . . . 14595, heated, 604.

232

Do. . . . . . . . . 14595, heated, 604.

Note that the second image of No. 232 is in reflected light.

233

Do. . . . . 107 - heated, 14598, Do. reheated 14603, 25, 74, 6.

Note that the second image of No. 233 is in reflected light.

234 to 243. Voltaic deflagrations, Gold terminals, 14664, 75.

235, 237, 239. Voltaic deflagrations, heated 14885

234

The first of Faraday's "deflagrations," deposits formed by exploding thin wires with rapid bursts of electricity.

235

236

The last image (at roughly 20x) shows the rich variety of colors obtained, but not green. See entry 14665, 9 April 1856.

237

238

239

240

Faraday noted "a green ... though the green was not good" (entry 14667, 9 April 1856). No green was visible to the editor, however.

241

Damage to the slide is apparent in this image.

242

243

No. 243 is broken.

244, 245. Gold films by phos., 14681, 3.

244

Faraday used Nos. 244 and 245 to test the conductivity of the films. Both conducted, as expected.

245

246, 247, 248. Do. . . . with borax, 14683, and heated.

246

Nos. 246-248 were treated with borax (a flux) and also tested for conductivity.

247

Faraday noted No. 247 was "quite green" when pressure was applied. This is barely visible by examination.

248

249

Do. . . . no borax, but heated, 14683.

Faraday noted "a fine ruby effect added here and there" under reflected light (entry 14683, 12 April 1856).

250

Do. . . . 14684, with borax.

251, 252, 253. Do. . . with borax and heated, 14684.

251

252

253

254

Do. . . no borax, 14684, 5.

255

Very thin film, 14686.

"These fine films are very interesting" (entry 14686, 12 April 1856, referring to Nos. 255-258).

256, 257, 258. Do. . borax and heat, 14686, fine ruby tint.

256

Ruby tints are barely visible around the edges of Nos. 256, 257 and 258.

257

258

259, 260 - medium gold film, 14687, 8, 5238.

259

260

261

Do. . . . . . heated, 14688.

262, 263, 264 - with borax, heated, 14688.

262

263

264

265, 266, 267 - films, no borax, 14690.

265

266

267

268, 269, 270, 271 - films with borax, 14690.

268

No. 268 is broken. Note the clear ruby color at the left.

269

270

271

267, 268, 269, 270 [sic] - films heated, 14690.

NB: These numbers are repeated and refer to the slides above after being heated.

272, 274 - film not heated, 14691.

NB: No. 274 is listed below.

272

273, 275, 276 - films, borax and heated, 14691.

273

"Agate pressure effect very good" i.e.,"changing ruby to green" (entry 14691, 12 April 1856), but barely visible here.

274

275

276

277 to 300 – films and rings from surface of standing solution, 14694, 707, 11.

277

This series (277-300) was produced by letting bits of phosphorous float overnight on a weak gold chloride solution. Thin rings of gold were formed around the phosphorous then lifted off onto the slides. See entry 14694, 13 April 1856.

278

279

280

No. 280; see below, after No. 354.

281

No. 281; see below, after No. 354.

282

283

284

285

286

287

288

289

No. 289; See below, after No. 354

290

291

No. 291 is chipped.

292

293

294

295

296

297

298

299

300

301 to 318. Do. 14697, 11, 5238.

301

Nos. 301-318 continue the series of "films and rings of standing solutions" that began with No. 277.

302

No. 302; see below, after No. 354.

303

304

305

No. 305; see below, after No. 354.

[This series continued in next box]

Box 306-385

[Series continued from last box:]

301 to 318. Do. . . . . . . . . . . . . 14697, 11, 5238.

[i.e.,"films and rings from surface of standing solution, 14694, 707, 11."]

306

307

No. 307; see below, after No. 354.

308

309

310

No. 310; see below, after No. 354.

311

312

313

314

No. 314; see below, after No. 354.

315

No. 315 is on paper.

316

317

No. 317 is on paper.

318

319 to 340. Deflagrations of gold wires, 14699, 708, 12.

319

320

321

No. 321; see below, after No. 354. These deflagrations were produced using a battery of Leyden jars and are much better than the earlier series (Nos. 234-243 above). The earlier series used voltaic batteries.

322

No. 322 shows an intense ruby color most visible in the last, overexposed, image.

323

No. 323 is broken.

324

325

326

327

No. 327; see below, after No. 354.

328

329

330

331

Nos. 331 and 332 show a "two fold course" perhaps due to a discharge "carried across by gold spread abroad by the first course" (entry 14700, 14 pril 1856).

332

333

334

No. 334; see below, after No. 354.

335

336

337

338

339

No. 339 is broken.

340

No. 340 is on paper; 2 examples.

341 to 354, Deflagrations of silver wire, 14702, 9, 13, 5262.

341

Note that deflagrations of silver wire are much less colorful than those of gold wire. See entry 14702, 14 April 1856.

342

343

No. 343 is broken; see below, after No. 354.

344

345

346

347

No. 347; see below, after No. 354.

348

349

350

No. 350; see below, after No. 354.

351

352

This slide does show some traces of green, as Faraday noted (entry 14702). But the deposit, as he also noted, "is very loose," so these may not have been as well preserved as the gold preperation.

353

354

No. 354 is broken. Some green is visible here.

280, 1, 9, 302, 5, 7, 10, 14 - gold films, heated, 14711.

321, 7, 34. Gold deflagrations, heated, 14712, 5240, 58.

343, 7, 50. Silver deflagrations, heated. 14713.

355, 6, 7, 8. Thick gold films by phos., heated, 14715, 20.

355

356

357

358

359-367. Gold films by phos., much borax, heated, 14717.

359

See entry 14717, 17 April 1856. Faraday made these from "standing rings," as before, but treated them with "much borax" before drying.

360

No. 360 is broken.

361

362

363

364

365

366

367

368-375. Gold films, thick and thin, 14721.*

The asterisk is Faraday's to signal a slight error in numbering Diary entries.

368

Some green or turquoise is visible in these films, but it does not show well in the images.

369

370

371

372

373

374

375

376-383. Do. . . . . . . . 14723*.

376

377

378

379

380

381

382

383

[There are no slides bearing the numbers 384 or 385, nor are these numbers used in the Diary.]

Box 100-120; 386-405

See above for slides 100-120.

386-393. Gold explosions in oxygen, some heated, 14835-41, 5261, 3.

386

No. 386 [glass] is marked "Ox." This series of deflagrations was carried out under different gases to determine if the colors were due to compounds of gold. "The effects were precisely the same" (entry 14836, 1 July 1856).

387

No. 387 [glass] is marked "Ox" and "heated."

388

389

No. 389 [mica slip] is marked "Ox."

390

No. 390 [mica slip] is marked "Ox." Faraday also varied the substrate -- glass, mica and card.

391

No. 391 [mica slip] is marked "Ox" and "heated."

392

No. 392 [mica slip] is marked "Ox" and "heated."

393

394-399. Do. . . . . air, Do. . . . 14835-41, 5261.

394

No. 394 [glass] is marked "air."

395

No. 395 [broken] is marked "air" and "heated."

396

397

398

No. 398 [mica slip] is marked "air" and "heated."

399

400-405. Do. . . . . hydrogen, Do. . . . 14385-41

400

No. 400 [glass] is marked "hyd."

401

No. 401 [glass] is marked "hyd" and "heated."

402

403

No. 403 [mica slip] is marked "hyd."

404

No. 404 [mica slip] is marked "hy."

405

No. 405 [folded card] is marked "hydrogen," but no deposit is evident.

Box 406-464

406-410. Green films by phosphorus, 15065.

406

This series is notable for the very clear green color manifest around the edges of the circular patterns.

407

408

409

410

No. 410 is broken. This slide was heated; see entry 15073, 11 October 1856. "Agate pressure applied to the thin part developed most beautiful green and reflective power – finest I have seen."

411

Jelly with gold sol. - blue, 15076, 343.

No. 411 is marked "15076." This and other watch glass specimens were kept in a separate box but numbered as part of the slide series. They are the dried remains of gelatinized gold colloids

412

Do. . . . gold surface, blue, 15077, 343.

413

Do. . . . very little color, 15078.

414

Jelly alone, 15079.

415

Jelly and gold sol., fine ruby, 15079.

416

Do. . . . . . blue pale, 15080, 343.

417-424. Ruby jellies dried on glass, 15155, 342.

There are 5 similar specimens in small "Ruby Jellies" box in the Long Box.

417

See 15155; 417 is a watch glass.

418

See 15155; 418 is a watch glass.

419

See 15155; 419 may be a watch glass.

420

See 15155; 420 is a watch glass.

421

No. 421 is marked "6." These are also jellies but mounted on glass slides.

422

No. 422 is marked "5."

423

No. 423 is marked "7 [?]."

424

No. 424 is marked "8."

425

Beaker ruby for rotation results (15166)

Apparently not a slide.

426, 427. Cells for blue and ruby fluids (15168, 15211).

See below; misnumbering here?

426

See entry 15211; appears to be gold leaf in a cell of two slides.

427

428 to 432 — films of jellies dried, 15228, 32.

428

See 15168; appears to be a blank cell, jelly deposit faintly visible.

NB: There are three slides numbered 428, one a possible film of dried jelly, one a cell of two slides with a blue deposit and one a two-slide cell of dried jelly (shown above). There are two slides numbered 429, one a two-slide cell with a blue deposit and one a possible dried jelly.

429

Two slides bear this number. One appers to be a blank slide, and the other is a cell with a jelly deposit. See entry 15168, 20 October 1856.

430

431

Like 428-9; jelly deposit faintly visible.

432

Like 428-9; jelly deposit faintly visible.

433, 434. Arsenic triturated. 15184, 220.

"Triturated" means pulverized. Thus, these slides were simply dried powders and would be unlikely to survive.

433

434

435

Bismuth, triturated. 15184, 220.

436, 437. Antimony triturated. 15184, 220.

436

437

438, 439. Purple of cassius, XLVIII. 15184, 221, 9.

"Purple of cassius" is a gold and tin oxide used to give a ruby color to glass.

438

439

440, 441. Blue deposit by salt, LXXI. 15184, 222, 30, 93.

It is not clear what "Blue deposit by salt" means here. Perhaps the result of "poisoning" a colloid?

440

No. 440 marked "LXXI."

441

No. 441 marked "LXXI."

442

Palladium films, many. 15185, 215, 9.

Each No. 442 is marked "Pal." There are seventeen of these, of which two are shown. They were produced by floating phosphorous on a solution of chloride of palladium. The transmitted color was "Indian ink, from faintest shade up to blackness" (entry 15185, 22 October 1856).

443 to 447. Fine gold leaf. 15183, 4, 214, 36, 59, 72.

Each is marked "F."

443

These are commercial gold leaves, and all are quite thick.

444

445

446

447

There are three slides marked No. 447.

448

Silver films, many. 15188, 216, 9, 65.

Each No. 448 is marked "S." There are 11 of these; two are shown. They were produced by floating phosphorous on silver nitrate (entry 15188, 22 October 1856).

449

Platinum films, many. 15189, 217.

Each No. 449 is marked "Plat" or "Pl." There are 8 of these, marked "1" through "8." The deposits on all are very faint. Compare to slide No. 85, above.

450

Platinum film rubbed up into powder. 15189.

The powder would be unlikely to survive.

451

Rhodium film. 15190, 3, 218.

There are four of these, one submarked "2" and "Rhod," the others marked "R." Only one is shown. The second image is in reflected light to show the bright metallic sheen.

452

Sulrt. Palladium. 15198.

There are three of these, submarked "S of P." These and the following were "sulphuretted" in an atmosphere of hydrogen sulfide (entry 15197, 22 October 1856). "I doubt whether there is any sulphur in it but we shall see" (entry 15198, 22 October 1856).

453

ulrt. Silver. 15199, 228 [a].

here are three of these, submarked "S of S" (deposits very faint). From silver nitrate.

454

Sulrt. lead. 15200, 26.

There are three of these, submarked "S of L." From lead nitrate.

455

Sulrt. antimony. 15201, 23.

There are two of these, submarked "S of A." From "Sol. Emetic tartar-antimony."

456

Sulrt. copper. 15202, 24, 64, 73, 4.

There are three of these, all submarked "S of C" and submarked "1," "2" and "3." "Sol. Acetate copper."

457

Sulrt. Mercury? 15203, 25.

There are two of these, submarked "S of M" and "1" and "2." From "Sol. CO2 Sublimate."

458

Sulrt. Platinum? 15204.

No. 458 is submarked "S of Plat." "Sol. Chlo. Platinum."

459

Sulrt. Gold? 15205, 27.

No. 459 is submarked "S of G." "Sol. Chlo. Gold."

460, 461. Deposit of LXXXIII C, dried on glass. 15231, 68.

460

No. 460 is marked "LXXXIII c." See entry 15023, 19 September 1856. "LXXXIII" is a fine ruby fluid, i.e., a gold colloid.

461

No. 461 is marked "LXXXIII c."

462

Film of Gold by hydrogen. 15241.

No. 462 is submarked "1." Faraday prepared a variety of films by placing solutions in an atmosphere of hydrogen.

463-466. Films of palladium by hydrogen. 15242, 67.

463

No. 463 is marked "II."

464

No. 464 is marked "II."

Box 465-560

463 - 466. Films of palladium by hydrogen. 15242, 67.

See previous.

465

No. 465 is marked "II."

466

No. 466 is marked "II."

467 - 470. Films of rhodium by hydrogen. 15243, 66.

467

468

No. 468 is marked "III."

469

No. 469 is marked "III."

470

No. 470 is marked "III."

471, 472. Films of silver by hydrogen. 15244.

471

No. 471 is marked "IIII."

472

No. 472 is marked "IIII."

473 - 477. Platinum films by hydrogen. 15245, 69.

473

No. 473 is marked "IIIII."

474

No. 474 is marked "IIIII."

475

No. 475 is marked "IIIII."

476

No. 476 is marked "IIIII."

477

No. 477 is marked "IIIII."

478 - 480. Gold films by hydrogen. 15254.

478

No. 478 is marked "G."

479

No. 479 is marked "G."

480

No. 480 is marked "G."

481 - 483. Palladium films. Do. 15255.

481

No. 481 is marked "II."

482

No. 482 is marked "II."

483

No. 483 is marked "II."

484 - 485. Silver films by hy. 15256.

484

No. 484 is marked "IV."

485

485 is marked "IV."

486-488. Iridium films by hy. 15257, 65, 70.

486

No. 486 is marked "VI."

487

No. 487 is marked "VI."

488

No. 488 is marked "VI."

489 - 494. Jelly, ruby, etc. with gold. 15278.

489

See entry 26389, 27 October 1856. These were watch glasses, not slides.

490

491

492

Nos. 492-494 are watch glasses in another box.

493

494

495, 496. Gold leaf heated in oil tubes. 15284, 307.

495

496

497 - 505. Gold leaf on plates heated at a gas lamp. 15292, 308, 38.

497.

498

499

"In 12' [minutes] the green color is gone" (entry 15292, 30 Ocober 1856).

500

501

502

503

504

505

506 - 508. Do. . . . . heated in an oil bath. 15295, 309, 10, 1, 38, 51.

506

507

508

carelessly rubbed off

No. 508 lacks the gold leaf; see entry 15309, 31 October 1856; "carelessly rubbed off, and it is kept for another reason" (see entry 15321, 1 November 1856).

509 - 511. Two and three golds on glass, heated, lamp. 15312.

509

510

511

512 - 514. Fine gold leaf on mica, heated. 15314.

512

"They changed and lost the green colour just as before – so the glass is not the cause of the change" (entry 15314, 31 October 1856).

513

514

515

Fine gold leaf on rock crystal, heated. 15315.

516 - 517. Fine gold leaf on platinum and silver, heated. 15316, 7.

516

Note that the gold leaf is mounted on both sides.

517

This was gold leaf on silver. See entry 15317, 31 October 1856.

518 - 523. Copper defln. in hydrogen. 15324, 5.

518

This long series represents the deflagration of wires under hydrogen between two glass plates. They were examined quickly "before any time for oxidation had occurred" (entry 15323, 1 November 1856).

519

520

521

522

523

524 - 529. Palladium Do. . . . 15326.

524

525

526

No. 526 is marked "IX."

527

No. 527 is marked "X."

528

No. 528 is marked "XI."

529

No. 529 is marked "XII."

530 - 532. Platinum Do. . . . 15327.

530

No. 530 is marked "III."

531

No. 531 is marked "XIV."

532

No. 532 is marked "XV."

533 - 538. Iron Do. . . . 15328.

533

No. 533 is marked "XVI."

534

No. 534 is marked "XVII."

535

No. 535 is marked "XVIII."

536

No. 536 is marked "XIX."

537

No. 537 is marked "XX."

538

No. 538 is marked "XXI."

539 - 544. Lead Do. . . . 15329.

539

No. 539 is marked "XXII."

540

No. 540 is marked "XXIII."

541

No. 541 is marked "XXIV."

542

No. 542 is marked "XXV."

543

No. 543 is marked "XXVI."

544

No. 544 is marked "XXVII."

545 - 550. Tin Do. . . . 15330.

545

No. 545 is marked "XXVIII."

546

No. 546 is marked "XXIX."

547

No. 547 is marked "XXX."

548

No. 548 is marked "XXXI."

549

No. 549 is marked "XXXII."

550

No. 550 is marked "XXXIII."

551 - 554. Aluminium Do. . . . 15331.

551

No. 551 is marked "XXXIV."

552

No. 552 is marked "XXXV."

553

No. 553 is marked "XXXVI."

554

No. 554 is marked "XXXVII."

555 - 560. Zinc Do. . . . 15332.

555

No. 555 is marked "XXXVIII."

556

No. 556 is marked "XL."

557

No. 557 is marked "XLI."

558

No. 558 is broken (no Roman number).

559

No. 559 is marked "XLII."

560

No. 560 is marked "XLIII" and appears blank; lost film?

Box 561

An unidentified thin slide has slipped down the side of this box and cannot be removed without damaging either the box or the slide.

No. 504. Heated gold in chlorine gas. 15345.

See above for No. 504, which is, however, missing. Faraday provides an interesting description of this slide; see entry 15345, 4 November 1856.

Nos. 561-5. Copper films by oil. 15346.

561

See entry 15322, 1 November 1856. Faraday placed copper oxide in oil then heated this; copper films were produced.

562

563

564

565

566, 567. Do. . . . coarse. 15346.

566

567

568 - 570. Double copper films. 15346.

568

These three slides have films on both sides.

569

570

571, 572. Dry gold jelly, blue on surface, No. 1. 15114, 349.

571

Note that all watch glass specimens were kept in a separate box.

572

573, 574. Dry gold jelly, violet, No. 2. 15114, 349.

573

Note that most of the deposit has flaked off.

574

575, 576, 577. Dry gold jelly, salt, No. 3. 15114, 349.

575

576

577

578, 579, 580. Do. . . . salt, brown gold down, No. 4. 15114, 349.

578

579

580

581, 582, 583. Do. . . . blue, No. 5. 15114, 349.

581

582

583

584, 585, 586. Do. . . . fine ruby, No. 6. 15114, 349.

584

585

586

There appear to be two versions: one a deposit on card, and one a watch glass.

587, 588, 589. Do. . . . blue, salt., No. 7. 15114, 349.

587

No. 587 is a mounted watch glass in the "Roscoe Gift" box.

588

589

590, 591, 592. Do. . . . fine ruby, No. 8. 15114, 349.

590

591

592

593, 594, 595. Do. . . . very poor, salt. No. 9. 15114, 349.

593

594

595

596, 597, 598. Do. . . . very poor, No. 10. 15114, 349.

596

597

598

599

Gold leaf heated in pure oil. 15352.

600, 601, 602. Gold leaf on rock crystal, heated at lamp. 15353.

600.

601.

602.

603-608. Gold leaf on glass in Muffle. 15356.

603

604

No. 604 is marked "fine."

605

606

607

608

609

Silver leaf on glass in Muffle. 15357.

610

Rock crystal and gold sol., heated. 15358.

No. 610 is in the "Brown Paisley" box.

611

Do. . . . and gold leaf, much heated in Muffle. 15359.

612, 613, 614. Do. not so much heated. 15368, 70, 2.

612

No. 612 is in the "Brown Paisley" box.

613

614

No. 614 is in the "Brown Paisley" box.

615

Silver leaf on R. crystal, heated in Muffle. 15368.

616, 617. Silver leaf heated in Muffle. 15370.

616

617

618

Do. . . heated on surface to fusion. 15370.

619

Do. . . in alcohol for powder. 15370.

620

Tube and silver leaf, 6 leaves. 11373.

[Sic; probably entry 15373 was meant.] No. 620 is in the 'Ugues' box.

621, 622, 623, 624. Fine Golds on R. Crystal, in muffle. 15375.

621

622

No. 622 is in the "Brown Paisley" box.

623

624

625, 626, 627, 628. Silvers on R. Crystal, in muffle. 15375.

625

No. 625 is in the "Brown Paisley" box.

626

627

628

629 - 635. Gold wire deflagrated in hydrogen. 15403.

629

"Made more deflagrations of gold wire in hydrogen – letting the wire soak in this hydrogen for some hours beforehand. Ruby, green, etc. just as the former specimens" (entry 15403, 20 December 1856).

630

631

632

633

634

635

The ruby color is most evident in this slide.

636-641. Ruby jelly made for F.E. June 1857.

Last diary entry on this topic, dated 20 December 1856. "F.E." refers to the "Friday Evening" discourse. Faraday gave two lectures on gold at the Royal Institution: one on 13 June 1856, and one on 12 June 1857. His talk to the Royal Society was on 5 February 1857.

636

637