314 Dr. Ure nn Prussir Acid. 



sic acid present. By weighing out beforehand, on a piece of 

 paper, or a watch glass, forty or fifty grains of the peroxide, the 

 residual weight of it shews at once the quantity expended. 



The operation may be always completed in five minutes, for 

 the red precipitate dissolves as rapidly in the dilute prussic 

 acid, with the aid of slight agitation, as sugar dissolves in 

 water. Should the presence of muriatic acid be suspected, 

 then the specific gravity of the liquid being compared with the 

 numbers in the above table, and with the weight of peroxide 

 dissolved, will shew how far the suspicion is well founded. 

 Thus, if 100 grains of acid, specific gravity 0.996, dissolve more 

 than 12 grains of the red precipitate, we may be sure that the 

 liquid has been contaminated with muriatic acid. Nitrate of 

 silver, in common cases so valuable a re-agent for muriatic 

 acid, is unfortunately of little use here ; for it gives with prussic 

 acid, a flocculent white precipitate, soluble in water of ammonia, 

 and insoluble in nitric acid, which may be easily mistaken by 

 common observers, for the chloride of that metal. But the 

 difference in the volatility of prussiate and muriate of ammonia, 

 may be had recourse to with advantage ; the former ex- 

 haling at a very gentle heat, the latter requiring a subHming 

 temperature of about 300° Fahrenheit. After adding ammonia 

 in slight excess to the prussic acid, if we evaporate to dryness 

 at a heat of 212°, we may infer from the residuary sal-ammo- 

 niac, the quantity of muriatic acid present. 



The preceding table is the result of experiments which I 

 made some time ago at Glasgow. I have lately verified its 

 accuracy by experiments made at the Apothecaries' Hall, 

 London, on their pure prussic acid. 100 grains of the bi-cyanide 

 of mercury, require for their conversion into bichloride (corro- 

 sive sublimate), 28.56 grains of chlorine, a quantity to be found 

 in 100 grains of muriatic acid, specific gravity 1.1452. And as 

 100 grains of the bi-cyanide contain 20.6 of real prussic acid, 

 they will furnish, by careful distillation on a water-bath, a 

 quantity of liquid acid, equivalent to 700 grains of the medicinal 

 strength 0.996. By consulting my table of muriatic acid, pub- 

 lished in this Journal for January last, the quantity of it at any 



