100 



CHEMISTRY. 



Crystallized Hydrate of ChloroTiydric Acid. 

 In a communication to the Paris Academy 

 of Sciences, Messrs. Pierre and Puchot ob- 

 serve that, when a saturated solution of hydro- 

 chloric-acid gas is cooled to 21 or 22 C., 

 the dry gas being passed continuously into the 

 liquid, the temperature soon rises to 18, 

 and an abundant crystallization begins, the 

 temperature remaining constant at 18. Be- 

 fore the crystallization commences, there is 

 always a reduction of 3 or 4 in temperature. 

 Synthetic experiment showed that, to produce 

 the crystals, the water absorbed about its own 

 weight of the gas. The probable formula 

 would therefore be HOI (H 2 S ). In the air 

 the crystals decompose readily, emitting dense 

 fumes of hydrogen chloride. In a flask kept 

 near 0. they slowly melt, the temperature 

 remaining at 18. Water dissolves them 

 readily. As they sink in the solution in which 

 they are formed, they must be denser than it. 

 In the analysis a known weight of the drained 

 crystals was treated with a definite quantity 

 of distilled water, in amount sufficient to pre- 

 vent the evolution of gas. The chlorine was 

 then determined in the solution, and from this 

 the ratio between the HOI and the H a O could 

 be calculated. In Cho first two determina- 

 tions the ratio was 1 : 2.19; in the second, 

 1 : 2.085 ; hence the authors conclude upon 

 the formula given above. 



Sensitiveness of Silver Bromide to the Green 

 Ray. Repeated experiments, made by Mr. M. 

 Carey Lea, have shown that 1. The sensitive- 

 ness of silver bromide to the different rays of 

 light is distinctly modifiable by the presence 

 of various bodies, colored or colorless ; and, 2. 

 That no relation can be traced between the 

 color of these bodies and the refrangibilities 

 of the rays, the sensitiveness to which is modi- 

 fied. During the past year Mr. Lea made the 

 action of the green rays a special study, pub- 

 lishing his results in the American Journal 

 of Science and Arts. To determine whether 

 there exists any red substance capable of in- 

 creasing the sensitiveness of the bromide to 

 the green rays, the author experimented with 

 fourteen different red pigments ; but not one 

 of these, with the single exception of coral- 

 line, produced the slightest increase of sensi- 

 tiveness. And, though coralline appears to 

 have this effect, it in reality forms no excep- 

 tion to the general rule, because its action on 

 green light may be destroyed without destroy- 

 ing its color. Of colorless, or nearly colorless 

 substances, eight, viz., potassic arsenite, ar- 

 gentic arsenite, salicine, codeia, morphia ace- 

 tate, tincture of capsicum, ammonium valerate, 

 and caffein, gave an increase of sensitiveness. 

 From this it would appear that it is not among 

 the colored but the colorless substances that 

 we must look for those capable of increasing 

 sensitiveness to green light. Eight other color- 

 less substances, viz., ammonium hippurate, mu- 

 cate and mulate, plumbic arsenite, phloridzin, 

 parabonic acid, tincture of aloes, and potassic 



formate, were indifferent, while the following 

 eleven distinctly diminished the sensitiveness 

 to green light, viz., brucia, strychnia, narcotin, 

 daturin, acid ammonium nitrate, peperin, gen- 

 tianin, podophyllin, aconitin, asparagin, and 

 berberin. The author's conclusion from these 

 premises is, that there exists no relation be- 

 tween the color of a substance and the color 

 of the rays to which it increases the sensitive- 

 ness of silver bromide. 



A New Test for Arsenic. A simple and 

 readily-applied test for arsenic, being a modi- 

 fication of Marsh's test, is offered by Dr. E. W. 

 Davy, of the Royal College of Surgeons, Ire- 

 land. Marsh's test, as is well known, rests 

 upon the fact that nascent hydrogen, in pres- 

 ence of certain arsenic compounds, gives rise to 

 arseniureted hydrogen, a gas which can be 

 very readily detected, even in very minute 

 quantities. Marsh's method consists in gener- 

 ating, in a suitable apparatus, hydrogen by the 

 actiqn of dilute sulphuric acid on zinc, and then 

 adding the arsenical compound in solution. 

 Arseniureted hydrogen is quickly evolved, 

 and a fine jet of the gas being ignited, and a 

 cold surface being placed on the top of the 

 flame, characteristic spots of metallic arsenic 

 are produced. The process is, however, sub- 

 ject to this disadvantage, that the acid and zinc 

 employed may themselves contain arsenic ; and 

 it is difficult to find either substance perfectly 

 free. Dr. Davy proposes the employment of 

 an amalgam of sodium as a means of gener- 

 ating the hydrogen, thus doing away altogeth- 

 er with the necessity of any acid, and using 

 two metals that are not liable to arsenical con- 

 tamination. The amalgam proposed by Dr. 

 Davy consists of one part by weight of sodium 

 to eight or ten of mercury. 



In applying the test, the suspected solution or 

 solid matter is placed along with a little water in the 

 bottom of a test-glass ; then add a small bit of the 

 amalgam, about the size of a grain of wheat ; and, 

 lastly, place without delay, on the top of the glass, 

 a piece of white filtering-paper or the cover of a 

 white-porcelain crucible moistened with a drop of a 

 dilute solution of nitrate of silver, slightly acidulated 

 with nitric acid, when if arsenic is present a dull- 

 black or deep-brown stain on the paper, or a dark 

 silvery one on the porcelain, will be quickly de- 

 veloped in the part moistened, owing to the silver 

 of the salt being reduced to the metallic condition 

 T>y the agency of the arseniureted hydrogen^ thus 

 evolved, which, coming in contact with, the nitrate 

 of silver, gives rise to the following reaction : 



H 3 As + 6 AgN0 3 + 3H 2 0=6HN0 3 + H 3 As0 3 + 3 Ag a . 



The silver solution is made by dissolving twenty 

 grains of the nitrate in an ounce of distilled water, 

 and then adding two drops of strong nitric acid to 

 render the solution slightly acid. A small disk of 

 bibulous paper, between the mixture in the glass and 

 the paper or cover moistened with the silver solution, 

 will intercept any particles of the liquid which might 

 otherwise be projected against them, producing 

 there minute black spots, and thus interfering with 

 the results of this test. 



Exceedingly minute quantities of arsenic can be 

 readily detected by this process : thus the 1-1, 000th 

 part of a grain of arsenious acid, dissolved in 1 c.c. 

 of distilled water, gives a very decided effect in 

 a few moments ; but much smaller quantities are 



