DR SAMUEL BROWN ON PARACYANOGEN. 



They are presented in the form of a list selected from many others, so as both 

 to exhibit the process of observation which led to the last of them, and illustrate 

 the conclusion deducible from the whole series, viz. that the greater the pressure, 

 up to a certain degree, under which the haloid is decomposed, the greater the 

 quantity of paracyanogen produced. Accordingly, although the two last may ap- 

 pear to supersede the rest, they would in reality be inconclusive as to the in- 

 fluence of gradually increased pressure without them. They are all described with 

 what may seem to be unnecessary minuteness, partly because they are the first 

 recorded experiments of their kind, and partly because it will be necessary to 

 make particular references to them in future communications. 



1. A quantity of bicyanuret was thrown on an iron plate, previously heated 

 to a temperature much higher than the point of decomposition of the salt, yet 

 considerably short of that at which paracyanogen enters into combustion. Decom- 

 position instantly ensued, and there remained a residue of nearly half the bulk of the 

 cyanuret employed, which was found to be paracyanogen by the appropriate tests. 

 This was repeated several times at different temperatures, within the same range, 

 and with the evident result, that the speedier the decomposition, i. e. the higher 

 the temperature at which it was effected, the greater the bulk of the solid nitro- 

 carbon product. This rude experiment led to the next, in which the pressure of 

 cyanogen passing through a capillary tube was partly substituted for quick de- 

 composition. 



2. Some cyanuret was introduced into a tube of German glass, sealed at one 

 end, which was then drawn out from two inches above the surface of the con- 

 tents into a very fine capillary, a foot and a half in length. The containing ex- 

 tremity was suspended in a large spirit-lamp flame till the decomposition was 

 completed. During the operation, the opening of the capillary was carefully 

 watched for cyanogen by a lighted taper, but no combustion or other evidence of 

 gaseous escape ever appeared, the great pressure given by the long capillary hav- 

 ing prevented freedom of passage. An apparently full proportion of mercury had 

 sublimed into the upper two inches of the wide part of the tube ; and there re- 

 mained below a quantity of brown matter, occupying nearly the same space as the 

 original cyanuret. The residue in this case consisted of paracyanogen, cyanogen 

 mechanically retained, and a few little globules of mercury, but not a trace of un- 

 reduced cyanuret. This trial was also repeated several times, and always gave 

 similar results : when the drawing of the tube was less capillary there took place 

 escape of cyanogen, and less paracyanogen was left. These two tentative experi- 

 ments conducted to the following attempts to obtain numerical results. 



3. A strong test-tube, weighing 117.1 grs., was charged with 14.9 grs. of cya- 

 nuret, equal to 132 grs. It was drawn out at two inches from the bottom to 

 about five inches, and an inch above this to a foot in length, neither of the draw- 

 ings being quite so fine as in the second experiment. Heat was now applied, 



VOL. XV. PART I. Z Z 



