34 Mr. Phillips's Reply to Dr. Hope. [July, 



In preparing i\\e submurias hydrargyria pnecipitatus, you order 

 the mercury to be dissolved by an equal weight of dilute nitrous 

 acid. Now observing this difference, and well knowing that 

 the preparation of the acetate and the chloride of mercury depend 

 upon the formation of protoxide, I certainly did imagine that 

 the same quantities of metal and acid were applicable to both 

 cases. You tell me, however, tbat the College are not inconsis- 

 tent in ordering an excess of nitric acid in one case, and not in 

 the other : for you state that the excess is " advantageous for 

 the one, and prejudicial for the other." 



Now the advantage which you state to be derived from using 

 the excess of nitric acid in preparing the acetate is, that it dis- 

 solves the subnitrate, which would otherwise be precipitated 

 with, and contaminate the product. For a moment I will admit 

 this reason to be valid ; but if it be so, what prevents the same 

 effects from being produced when a solution of muriate of soda 

 is used instead of acetate? I apprehend it is the addition of 

 water, and not the nature of the salt dissolved in it, which deter- 

 mines the precipitation of subnitrate of mercury ; if so, it appears 

 to me that you are inconsistent in not ordering the excess of 

 acid in preparing the chloride, as well as in forming the acetate 

 ofmercury. 



You will probably remember, that in analyzing calomel pre- 

 pared by precipitation, Mr. Chenevix actually found a quantity 

 of subnitrate ; I do not, however, mean to assert that the pro- 

 portions of mercury and acid which he used in preparing it were 

 such as are directed by you ; I mean merely to show that this 

 effect in some cases actually happens. 



I will again admit that the excess of acid is requisite to produce 

 the alleged effect ; but even in this case, I think it is employed 

 in a disadvantageous mode. 1 suppose you will agree with me, 

 that it is only the peroxide of mercury which is subject to be 

 precipitated in the state of subnitrate ; if so, the formation of this 

 oxide must be much increased by using one-half more and than 

 is requisite for the preparation of the protoxide. It seems to 

 me that this end would be quite as well answered, and with much 

 less chance of producing peroxide of mercury, if the solution 

 prepared with only the requisite quantity of acid were afterwards 

 diluted with water, with which the excess of acid had been 

 mixed ; in this mode, as it appears to me, it would retain its 

 power of redissolving subnitrate, without possessing that of form- 

 ing peroxide. 



In my analysis of your Pharmacopoeia, I stated that T procured 

 only 29 of acetate ofmercury from a solution of 72 of the metal. 

 I have since obtained a considerably larger product ; viz. 36 

 parts ; still, however, the loss of mercury is extremely great. 

 Upon a moderate calculation at least 44 parts of 72 of mercury 

 are unemployed in the formation of acetate ; and this proportion 

 I certainly am still of opinion that it would be advisable to save 



