152 Intelligence and Miscellaneous Articles. 



without adverting to the possibility of other volatile substances 

 being hereafter discovered to have a similar effect on solution of 

 silver, it is to be borne in mind that this reagent indicates the ex- 

 istence of prussic acid in some esculent substances where it had 

 previously been found, as well as in some new ones. Upon this 

 branch of the subject medical jurists will probably think it right to 

 collect information. 



The application of the solution of silver is simple. The suspected 

 fluid is to be acidulated by the addition of acetic acid, but so as to 

 redden litmus paper in only the slightest degree. If excess of acid 

 be already present, it is to be not quite neutralized by carbonate of 

 soda. These precautions are adopted to retard the interference of 

 ammonia or muriatic acid. Two or three drops, quite cold, are then 

 put into a watch glass, and immediately covered by a plate of glass, 

 whose under-surface, to the breadth of a pea, is moistened with so- 

 lution of nitrate ofsilver, formed by dissolving one grain lunar caustic 

 in 100 grains distilled water: — 



If the inverted drop of silver solution retain its transparency un- 

 altered, the absence of prussic acid is established ; for had it been 

 present, the silver solution would in a few moments have become 

 clouded by the formation of a white precipitate, an effect which, 

 indeed, is almost instantaneous when the prussic acid is not exces- 

 sively diluted. If, on the other hand, the precipitate appear, the 

 conclusion must not be drawn that it is cyanuret of silver, until iden- 

 tified as such by two properties : — first, its speedy re-solubility, as 

 denoted by the clouded drop becoming again clear, when placed 

 over a vessel of caustic ammonia, in which respect it differs from the 

 silver compounds of iodine and bromine: — and secondly, in retain- 

 ing unchanged its pure white colour after exposure a i'ew minutes 

 to the sun's rays, or for a longer time, to day-light. As this pro- 

 perty essentially distinguishes it from the compound ofsilver with 

 chlorine, it is important to establish it by a separate experiment 

 upon a somewhat larger portion of the precipitate, which should be 

 obtained, by candle-light, by successively placing the inverted drop 

 of nitrate of silver over renewed portions of the liquid in a saucer: 

 as soon as the precipitate separates into distinct curd-like particles, 

 it is ready for exposure to the solar rays. 



Another property which distinguishes the cyanide (or cyanuret) 

 ofsilver from the chloride, is, that upon being ignited in an open 

 short glass tube, the cyanogen burns with a flame of the usual 

 colour, leaving the metal pure, if sufficiently heated, — a quality the 

 more valuable as it furnishes an index to the proportion of prussic 

 acid it represents, which upon ordinary occasions may be estimated 

 as equal to one fourth [he weight of residual silver. 



When, acting upon this principle, it is desirable to ascertain the 

 entire quantity of prussic acid, it is to be obtained by slowly di- 

 stilling over, in nearly filled close vessels, about an eighth of the 

 acidulated mixture under examination; rectifying it; re-acidula- 

 ting by acetic acid; precipitating by slight excess of nitrate silver; 

 washing with distilled water, only so long as the washings affect 



