102 



POPULAE SCIENCE NEWS. 



[Jui.v, 1889. 



almost any neutral substance. So far I have not 

 found any that does not precipitate it. Not only 

 saline solutions do this, but even a solution of gum 

 arable. 



Neutral salts may precipitate the silver in either a 

 soluble or an insoluble form. Alkaline sulphates, 

 nitrates and citrates throw down the soluble form, 

 magnesium sulphate, cupric sulphate, ferrous sul- 

 phate, nickel sulphate, potassium bichromate and 

 ferro cyanide, barium nitrate, even silver nitrate and 

 other salts throw down a perfectly insoluble form. 

 The soluble form constitutes a blue or bluish black 

 precipitate; the insoluble, a purple brown, which 

 by repeated washing, by decantation or otherwise, 

 continually darkens. 



What is very curious is that the insoluble form 

 may be made to return to the soluble condition. 

 Many substances are capable of effecting this 

 change. Sodium borate does so, producing a brown 

 solution, potassium and sodium sulphate produce a 

 yellowish red solution and ammonium sulphate a 

 red one. None of these solutions has the same 

 blood-red color as the original solution ; the form of 

 silver seems to change with the slightest change of 

 condition. 



Sometimes the substance will spontaneously pass 

 into a soluble form. A specimen, rendered insolu- 

 ble by precipitation with ferrous sulphate, after 

 much washing began to run through, not only as a 

 suspension, which often happens, but as a solution, 

 clearing itself, after a day or two, of insoluble por- 

 tions and furnishing a rose-red solution. I have 

 kept this solution in a corked vial for eight months, 

 during which time it has remained unchanged. 



Analysis. — A specimen dried in vacuo over sul- 

 phuric acid gave : 



No. I . . . . 97.17 percent, silver. 

 No. 2 .... 97.10 " " 



A specimen dried first in vacuo and then at 100'^ 

 C., lost in the second drying .88 per cent, water. 



So that the substance dried at 100" contained 

 97.96 per cent, of silver. The remaining 2.04 per 

 cent, consisted of ferric oxide and citric acid. 



C. Gold- Yellow and Copper-colored Silver. 



It has been long known that golden-yellow specks 

 would occasionally show themselves in silver solu- 

 tions, but could not be obtained at will, and the 

 quantity thus appearing was infinitesimal. Proba- 

 bly this phenomenon has often led to a supposition 

 that silver might be transmuted into gold. This 

 \ellow product, however, is only an allotropic form 

 of silver, but it has all the color and brilliancy of 

 gold, a fact which was apparent even in the minute 

 specks hitherto obtained. 



By the means presently to be described, silver can 

 be converted wholly into this form. It is a little 

 curious that its permanency seems to depend en- 

 tirely on details in the mode of formation. I found 

 iiinnv ways of obtaining it, but in a few months the 

 s prcser\ed changed spontaneously to nor- 

 >er. This ii;ii>pencd even in well closed 

 1 he normal silver, produced 'in this way is 

 c.'vquisiLcly beauuiul. 1l has a pure and perfect 

 white color like the finest frosted jewelers' silver, 

 almost in fact exceeding the jewelers' best products. 

 I found, however, one process by which a quite per- 

 manent result could be obtained. Specimens made 

 by it in November of 1886 are now, at the end of 

 thirty months, unchanged. 



In forming the blue product which I have called 

 A, very concentrated solutions were necessary. C, 

 on the contrary, is best obtained from very dilute 

 ones. The following proportions give good results. 



Two mixtures are to be prepared : No. i, contain- 

 ing 200 c. c. of a ten per cent, solution of silver ni- 

 trate, 200 c. c. of twenty per cent, solution of 



Rochelle salt and 800 c. c. of distilled water. No. 

 2, containing 107 c. c. of a thirty per cent, solution 

 of ferrous sulphate, 200 of a twenty per cent, solu- 

 tion of Rochelle salt and 800 of distilled water. The 

 second solution (which must be mixed immediately 

 before using onlj') is poured into the first with con- 

 stant stirring. A powder, at first glittering red, 

 then changing to black, falls, which on the filter has 

 a beautiful bronze appearance. After washing it 

 should be removed whilst in a pasty condition and 

 spread over watch glasses or flat basins and allowed 

 to dry spontaneously. It will be seen that this is a 

 reduction of silver tartrate by ferrous tartrate. The 

 metallic silver formed by reduction with ferrous 

 citrate and ferrous tartrate is in an allotropic condi- 

 tion ; with ferrous oxalate this result does not seem 

 to be produced. 



Although the gold-colored silver (into which the 

 nitrate used is wholly converted) is very permanent 

 when dry, it is less so when wet. In washing, the 

 filter must be kept always full of water : this is es- 

 sential. It dries into lumps exactly resembling 

 highly polished gold, especially the surfaces that 

 have dried in contact with glass or porcelain. For 

 this substance has in a high degree the property 

 already described in forms A and B — that of drying 

 with the particles in optical contact. When the 

 thick pasty substance is extended over glazed paper, 

 it dries with the splendid lustre of gold leaf, with 

 this essential difference, that these allotropic forms 

 of silver B and C assume spontaneously in drying 

 the high degree of brilliancy which other metallic 

 surfaces acquire by elaborate polishing and burnish- 

 ing. By brushing a thick paste of this substance 

 evenly over clean glass, beautiful gold-colored mir- 

 rors are obtained ; the film seems to be entirely con- 

 tinuous and the mirror is \ery perfect. 



By continued washing the precipitate changes 

 somewhat, so that in drying it takes on a coppery 

 rather than a golden color, and is rather less lus- 

 trous, though still bright and permanent. 



Two silver determinations by conversion into 

 chloride made in November, 1886, gave : 



No. I . . . . 97.81 per cent, silver. 



No. 2 . . . . 97.86 " 

 Recently these experiments have been repeated 

 and the washing was more successful. Ferric tar- 

 trate adheres very obstinately and after a time wash- 

 ing with water ceases to remove it. Stronger means 

 cannot be employed without affecting the substance 

 itself These last determinations gave : 



No. I . . . 98. 750 per cent, silver. 



No. 2 . . . 98.749 " " 



The residue of No. 2 was examined and consisted 

 almost wholly of ferric citrate. 



PRACTICAL RECIPES. 



Indelible Anilin Ink is prepared as follows : 

 Two solutions are prepared separately: (i) Cop- 

 per chloride, 8.5 Gr. ; sodium chloride, 10.6 Gr. ; 

 amnionic chloride, 5.3 Gr. ; water, 60.0 Gr. (2) 

 Anilin chloride, 200 Gr. ; gum, 8.0; glycerine, 

 100 Gr. ; water. 42.0 Gr. One part of solution (i) 

 is mixed with four parts solution (2), when the ink 

 is ready for use. 



Iridescent Paper. — The following formula is 

 recommended, but we have had no opportunity ol 

 testing it, and can only give it for what it is worth : 

 Boil in water 8 parts (by weight) of nut-galls, 5 

 parts of sulphate of iron, 4 each of sal-ammoniac 

 and sulphate of indigo, and >» part of gum arable. 

 Wash the paper in this decoction, and then expose 

 it to the fumes of ammon a until the desired result 

 is reached. 



Light in the Photo<;rapiikr's Dark Ciiamhkr. 

 — The window of the dark chamber may be made of 



glass coated with the following composition : Ace- 

 tate of lead, 10 parts; water, loo parts; gelatine, 

 sufficient. Dissolve, and add with constant agita- 

 tion : Potassium chromate, 6 parts; potassium bi- 

 chromate, 4 parts. Another formula is the follow- 

 ing : Dissolve 5 parts of carmine in 40 parts of 

 water of ammonia. Mix water 450 parts, nitric 

 acid 2 parts, glycerine 7 parts, and dissolve in the 

 mixture 50 parts of gelatine; mix the two solutions, 

 and apply hot to the glass with a flat brush as many- 

 coats as may be required. The light is made more 

 pleasant by covering the window with one or two 

 thicknesses of thin yellow paper. 



Colored P'ire.s. — According to Siuld. Apothek. 

 Zig. the following mixtures produce lights of bril- 

 liancy equal to that of electricity. The cost of some 

 of the ingredients would be objectionable, and the 

 usual precautions against explosion should be taken. 

 The ingredients must always be pulverized sepa- 

 rately, and only mixed by carefully sifting together. 



While Fire. — Equal parts of sulfonal and potas- 

 sium chlorate in fine powder are carefully mixed. 

 Two grams furnish an intense light. 



Lilac Fire. — Lithium carbonate, 5 parts, and 20 

 parts each of sulfonal and potassium chlorate, each 

 in very fine powder, carefullv mixed. 



Violet Fire. — Magnesium metal, powdered, 8 

 parts; potassium bichromate, 10 parts, and potas- 

 sium permanganate, 16 parts, carefully mixed. 



LABORATORY NOTES. 



Testing Filtering Paper. — In testing filtering 

 paper, one feature, among others, should be specially 

 paid attention to, namely, the rapidity with which 

 liquid will spread over a given surface. This may 

 be ascertained tiy fastening to a frame a series of 

 equal strips of various filtering papers, and then 

 immersing then simultaneously in water. The 

 exact time of immersion being noticed, it only re- 

 mains to wait until upward diffusion stops, and then 

 to read off, on the scale to which each strip is fas- 

 tened, the degree or mark to which difl'usion ex- 

 tended. 



Standardising Permanganate.— Many analysts 

 still prefer to standardise their permanganate with 

 pianoforte wire, but the trouble always is to exclude 

 the air after the iron has dissolved. Jaiiode oper- 

 ates as follows: The iron is dissolved in boiling 

 acid in a flask, which is closed by a cork, through 

 which goes a doubly-bent tube, the end of which is 

 made to dip into a beaker containing a solution of 

 sodium bicarbonate. When solution is complete, 

 and the liquid allowed to cool, the soda solution 

 finds its way into the flask, but, no sooner have a 

 few drops got in, than an evolution of carbonic acid 

 gas drives the fluid back. 



On a Method of Avoiding "Bumping" in 

 Distillation. — Markownikoff has suggested the 

 use, in place of platinum wire, charcoal, etc., intro- 

 duced into solutions to prevent bumping during 

 ebullition, a few thin capillary glass tubes, three to 

 ten mm. in length, sealed at one end. Under these 

 circumstances the boiling goes on quietly, both at 

 the ordinary and at reduced pressures, even when a 

 finely divided precipitate like barium sulphate ex- 

 ists in a saline aqueous solution. Even caustic 

 soda solution may be made to boil quietly in this 

 way. Branner recommends that the tubes be made 

 of different sizes, so as to float in difltrent layers of 

 the liquid. For the c^stillation of concentrated 

 acids he has found this method invaluable. Another 

 method, suggested by Mr. S. E. Parkhill, is to 

 slightly roughen the interior surface of the flask, by 

 introducing fluor-spar and sulphuric acid, and evolv- 

 ing a little hydrofluoric acid in the usual manner. 



