DR SAMUEL BROWN ON PARACYANOGEN. 173 



ticity, commonly known as the law of BOYLE and MABIOTTE. A (fig. 1) is a very 

 thick and strong glass- vessel, somewhat of the shape and size of a common spirit- 

 lamp, with a strong tubular and well ground opening in one side. B is a brass 

 collar, an inch and a half in length, fitted closely round the neck of A with brazier's 

 cement ; the upper half of the interior of B is a female screw. C D (fig. 2) is a 

 barometer tube of the greatest strength which is made, thirteen inches long ; the 

 upper ten inches are graduated from above downwards, every inch being divided 

 into tenths ; at the tenth inch is fitted on the immoveable brass collar E, the part 

 e being cubic, and fitted with a detached crane-lever (fig. 3), ef being a round 

 disc fitting tightly down on the top of B, and d' being a male screw fitting that of 

 B. F (fig. 4) represents a thick glass tube-retort, the beak of which is nicely 

 ground into the tubular opening of A, fig. 1. 



The method of using this instrument is exemplified in the details of the 

 experiment. C D was filled with quicksilver, inverted and screwed at d' into the 

 collar B, a well cut and greased leather disc having been interposed between the 

 top of B and the under surface of d ; it was fastened with the aid of the crane- 

 lever K. Quicksilver had been previously introduced into A to the height of the 

 tubular opening, so that the open end of C D was now submerged. The apparatus 

 was thrown on its side and shaken gently till the quicksilver fell in C D to the ninth 

 inch. The tube-retort was charged with bicyanuret and adapted to the tubular 

 opening with an air-tight cement, the junction being likewise thickly luted with a 

 paste of gypsum and gum-arabic, which sets very hard. Having remained two 

 days in this condition, the retort was put in a jacket-tube, and surrounded by a 

 large spirit-flame till the reduction appeared to be completed. In the mean time 

 the quicksilver in the meter-tube was watched ; it steadily ascended with a velo- 

 city manifestly diminishing with the increase of the height, till in twenty minutes 

 it reached 5.1 in. where it stopped. The flame was now withdrawn, equilibrium 

 of temperature restored, and the quicksilver fell to 8.1 in. ; from which it was in- 

 ferred that the quantity of cyanogen which had been liberated was measured by 

 the ascent of 0.9 in. ; while the maximum pressure under which the decomposi- 

 tion had been effected was measured by the ascent of 3.9 in. The apparatus was 

 taken down, and it was found that the reduction had been finished, so that cyano- 

 gen is given off from bicyanuret of mercury as paracyanogen, when decomposed 

 under a pressure bearing the same proportion to that of one atmosphere, as 9 in. 

 of the meter-tube to 5.1 in., i. e. according to the law of elasticity, a pressure of 

 1.76 atmospheres. The phenomenon may, for all that this and similar experi- 

 ments can determine, take place at lower degrees of tension, but I do not know 



how the minimum may be estimated. 







IV. Practical Observations. 1. Such are the experiments which have been 

 made on the transformation of cyanogen by fire. As processes, they contain 



VOL. XV. PART I. 3 A 



