1821.] Mr. Phillips'? Reply to Dr. Hope. 35 



first by the addition of solution of muriate of soda, so as to obtain 

 calomel, and then by adding potash to procure peroxide. 



Wishing, however, to determine, whether when mercury is 

 dissolved without heat in an equal weight of your dilute nitrous 

 acid, any subnitrate of mercury is actually precipitated with the 

 acetate,' I added to a solution thus prepared the requisite quan- 

 tity of acetate of soda dissolved in only haif the quantity of 

 water which you direct. The acetate of mercury, instead of 

 weighing only six parts from 12 of mercury, as by your process, 

 amounted to 11 parts; and the only important difference between 

 the products, if indeed it can be called one, was, that by using a 

 smaller quantity of water, the precipitate was rendered less 

 bulky, in order to determine whether it contained any subni- 

 trate, I boiled some of it in muriatic acid ; calomel was of course 

 formed and precipitated ; to the filtered solution I added 

 ammonia, which did not, however, cause any precipitation ; 

 whereas, if the acetate had contained any subnitrate, it would 

 have been decomposed by, and dissolved in the muriatic acid, 

 and the permuriate formed would have given the weil-knowu 

 white precipitate with ammonia. On repeating this experiment 

 I obtained rather a larger product of acetate. From these ex- 

 periments, therefore, I am of opinion that it is not requisite to use 

 the excess of acid which you have ordered, but that this acid con- 

 verts a large portion of mercury into peroxide which is of no use 

 in forming the acetate, and that it also diminishes the product, 

 by dissolving the acetate of mercury actually formed. If it be of 

 any consequence that the acetate of mercury should be extremely 

 light, it would be better to redissolve and crystallize it, than 

 occasion, what appears to rne to be, waste by your process. 



Oxidant Hi/drargi/ri, Pracip/tati;m. — I have already acknow- 

 ledged the error which 1 committed with regard to the quantity 

 of lime contained in the lime water, ordered for the decomposition 

 of the calomel in this process. But Mr. Dalton has observed, 

 and I have repeated and proved the accuracy of his experiments, 

 that lime water, prepared in different modes with respect to 

 temperature, contains very different proportions of lime. Under 

 these varying circumstances, I confess I do not consider it to be 

 an eligible substance for the purpose to which it is applied in this 

 process. If the lime be redundant, it will be precipitated by the 

 heat, and mix with the oxide of mercury ; if, on the other hand, 

 it be deficient, it will leave some calomel intermixed with the 

 oxide. Added to this, protoxide of mercury, at a very moderate 

 elevation of temperature, readily absorbs oxygen ; so that a por- 

 tion of it passing to the state of peroxide, the precipitate becomes 

 of a greenish colour, and is a mixture of the two oxides. 



I find that when potash is used, ncne of these inconveniences 

 follow. The calomel is decomposed even without the assistance 

 of heat, and a few ounces of solution of potash are as effective as 

 an equal number of pints of lime water. To some of the oxide 



d2 



