CHEMISTRY. 



I, aivordin:,' to tho just logic Of 

 :i elementary Milrstaiioc." 



of A to/ii i<- \\'i-i;i/ttH. Stas, 

 ,t.-d (J.-niiaii chemivi, has recently 

 in a largo quarto volume of 800 

 page- d by numerous engravings of 



atu.H used by him), the results of 

 's upon which ho has been engaged 

 1 u-ars. to determine the atomic 

 me of tho elements. 

 t!ie preparation of his materials he de- 

 i tin- greatest possible care, and every 

 <if hN invi .-illations was conducted with 

 tin ntnio-t nicety. His results agree in a sur- 

 prising manner with the numbers obtained by 

 Marignac by simple methods, and also with 

 f.iiiinl by Stas in his earlier experiments 

 for th' -aine purpose. The following are the 

 .v numbers for the atomic weights deter- 

 mined I iy him in these later and more complete 

 investigations : 



The veasels used in most of the experiments 

 were made from a special glass, composed of 

 the following mixture: silica 77.0, potash 7.7, 

 soda 5.0, lime 10.3=100. Only the purest 

 materials were used for this glass. It was 

 found to resist in the most powerful manner 

 the action of concentrated acids. A pound of 

 he most concentrated nitric acid being evapo- 

 t'roin a flask made of this glass, the flask 

 was found to have lost only a milligramme in 

 it. Melting nitre caused no loss of weight. 

 Tlu- water employed in the experiments was 

 freed from organic substances by being distilled 

 with manganate of potash. The condensing 

 tube of the still was made of platinum. 



Mr. Stas's mode of preparing pure silver may 

 be quoted as an instance of his 'attention to de- 

 tail>. His silver was obtained partly by the re- 

 duction of chloride of silver by milk-sugar and 

 pota-li, but more advantageously by precipita- 

 tion with sulphate of ammonia. For this pur- 

 pose silver coin is dissolved in nitric acid, 

 and the solution evaporated to dryuess, the 

 refine fused in order to decompose any 

 mixture of platinum salts, then dissolved in 

 ainiiioniacal water, and mixed with the requi- 

 .-ite quantity of sulphite of ammonia. The 

 reduction takes place slowly in the cold, more 

 rapidly when heated to 60-7G. The solution 

 iiiust be so dilute that it does not contain 

 more than two percent, of silver. 



The precipitated silver is washed with ain- 

 inoniacal water, and then concentrated ammo- 

 nia is poured upon it. On standing in the air 



tho liquid ought not to become blue ; if it doe*, 

 some silver is dissolved. As much as six 

 pounds of silver were worked up at once-. In 

 onler to test its purity, it was heated on a 

 lime support in tho oxyhydrogen blowpip.-, 

 where it fused without being covered with any 

 spots, began to boil with evolution of a bright 

 blue vapor (a greenish vapor indicates the 

 presence of copper), and finally distilled with- 

 out leaving any residue. Distillation is re- 

 garded by the author as the best means of 

 obtaining pure silver. Large burettes were 

 used for estimating the silver solution, and were 

 kept in a reservoir of water always at the same 

 temperature. The normal solutions were 

 placed in a perfectly darkened room, which 

 was lighted by a gas-lamp with a yellow screen. 

 Determinations of silver by diffused daylight, 

 according to the author, never give accurate 

 results. The estimation was effected in a black 

 box provided with a slide, lighted by a lamp 

 whose light passed first through a round flask 

 filled with a solution of neutral chromate of 

 potash. Ten grammes of the pure silver 

 were dissolved at a time and mixed with 

 normal solution of chloride of sodium (con- 

 taining 5.42 grammes), and the excess of the 

 silver dissolved determined by means of the 

 normal solution. The percentage of pure 

 silver was found=99.994 100.00 per cent, 

 mean 99.997. 



TJie Chemical Constitution of Fluorine Com- 

 pounds. M. Prat has made a valuable contri- 

 bution to chemical science in his researches into 

 the chemical constitution of fluorine compounds, 

 and the separation of the fluorine. He started 

 from the fact that the fluorides are really oxy- 

 fluorides; that the fluoride of calcium, for 

 example, is formed of two equivalents of cal- 

 cium, one of oxygen, and one of fluorine, and 

 that, in consequence, the true equivalent ot 

 fluorine is 29.5, and not 19., and that, in order to 

 obtain it, all that is necessary is to treat the 

 fluoride of calcium with chlorate of potash, or, 

 what is better, perchlorate of potash : for it is 

 only with this last salt that the reaction takes 

 place. Oxygen is disengaged, and a gas is pro- 

 duced which silver absorbs, giving rise to a 

 fluoride of silver, insoluble in water, soluble 

 in ammonia, from which it is precipitated by 

 nitric acid, and which is altered by the action 

 of light more rapidly than the chloride of silver ; 

 the formula of the real fluoride is Ag Fl., 

 whilst that of the soluble fluoride of the 

 chemists is Ag Fl, AgO. Fluorine is obtained 

 by heating, hi a platinum retort, fluoride of lead 

 of the chemists, one part, either with nitre five 

 parts, or with binoxide of manganese two parts. 

 Oxygen and fluorine are disengaged ; the oxygen 

 is taken up in its paasage by fragments of heated 

 baryta. Fluorine thus produced is nearly col- 

 orless, possessing an odor like chlorine, very 

 visibly giving off fumes in the air, incom- 

 bustible and heavier than air; it dissolves 

 indigo, reddens and discolors litmus-paper, 

 disengages fumes in contact with ammonia, 



