56 On the Combinations of fixed Oil with Nitric Acid, Sfc. 



The proportions as directed by the London College are, one 

 ounce of mercury, two ounces of nitric acid, six ounces of lard, 

 and four ounces of olive oil. I would recommend one ounce 

 of red oxide of mercury,* twelve drachms of nitric acid, six 

 ounces of lard, and four ounces of olive oil. I would combine 

 the lard with six drachms of nitric acid, using as gentle a he*t 

 as may be suflicient for the combination. For this purpose, 

 Laving mixed them together, they ought to be heated gently 

 till foam begins to form on the surface ; when, removing the 

 materials from the fire, they ought to be stirred for a few minutes 

 and allowed to cool. They ought then to be washed with 

 •water, and again cooled without agitation, when the fluid sinks 

 to the bottom, and may be removed by making an opening 

 through the materials, in order that the water may be poured 

 off. The remainder of the acid ought to be used to dissolve 

 the oxide of mercury, which, when evaporated to dryness, 

 ought to be triturated with the olive oil, and then the whole 

 melted together. Thus wo may obtain an ointment which 

 contains no uncombined acid or nitrate of mercury, and, in 

 short, similar to the ointment made in the common way when 

 washed. 



Having prepared an ointment in this manner, with pernitrate 

 of mercury, I attempted to form ono in the same way with 

 pronitrate of mercury ; but I found that the pronitrate was de- 

 composed, its acid being attracted by the lard and oxide being 

 separated, and when the mass was kept fluid subsiding to the 

 bottom. It therefore doe3 not form a compound, and ought 

 not to form an ingredient in the ointment. 



Pernitrate of mercury and laid, when triturated and exposed 

 together, did not form a chemical compound. The lard at- 

 tracted oxygen from the peroxide and combined with the acid, 

 the protoxide falling down as in the former case. 



I have observed also, that the red oxide having been tritu- 

 rated with an ointment suffers in the course of time decompo- 

 sition, for it became blue, and when melted deposited the pro- 

 toxide, but as this was a solitary case I do not know whether 

 it arose from accidental circumstances, or whether it was in 

 consequence of an alKnity which is in every case exerted be- 

 tween fixed oils and peroxide. 



Jf in preparing the ointment of nitrate of mercury rancid oil 

 or rancid lard is used, the ointment when formed consists of 

 two parts, which, when the mass is kept melted, separate from 

 each other, one similar in appearance to that procured from 

 fresh materials; the other, which is much heavier, more adhesive 



• As there is always a portion of pronitrate formed wlirn mercury is com- 

 bined with nitric acid, I prefer uiio^ tho red oxide which form* with uilrie 

 •cid prrnitmtc only. 



