-Jj§21.] of the Edinburgh Pharmacopeia. 191 



,,jacid than a smaller quantity ; and that there is no waste of ttie 

 solution, provided the filtration be practised as the Pharmaco- 

 pceia directs ; for by the successive affusions of water, the whole 

 of the solution is pushed through the hme. 



Subcarbonas AmmonicR, — You allege that two parts of carbon- 

 ate of lime are ordered when one and ahalfought tobe sufficient, 

 and that the excess requires the use of larger vessels and more 

 firing. The object of the excess in this case is to secure the 

 ..decomposition of the whole of the muriate, and save both time 

 j^nd fuel. 



Aqua J.m/Kom'^.-^This is a substance the preparation of whioh 

 Las been ordered in the different Pharmacopoeias in a variety of 

 ways. Though you particularly condemn our process, yet I am 

 persuaded, from many comparative trials, that it merits the pre- 

 ference. Your first objection lies against the excess of lime ; but 

 ..vnquestionably, in this instance, it is particularly useful, in acce- 

 lerating the disengagement of the ammonia, and rendering a less 

 , elevation of temperature necessary. You also complain that the 

 pungency of the odour on mixing and introducing the materials 

 into the retort causes much annoyance to the operator. The 

 ,pdour is unquestionably pungent, but if the operation be adroitly 

 ^p^naged, it causes no annoyance of the smallest consideration. 

 When the quantity of materials is not large, the mixture may 

 be made, and introduced so speedily, as to avert every inconve- 

 -nience ; and if it be intended that the charge of the retort shall 

 be considerable, it will require no great sagacity in the practical 

 chemist to discover, that he can mix the articles in as small por- 

 tions as he finds convenient, and introduce them in succession. 

 "While you give a preference to the formula of the London Col- 

 ,l§ge, you admit, that estimating by the strength of the product 

 merely, that of Edinburgh is more economical in the proportion 

 of 16 to 10; but you add, *' as, however, the Edinburgh order 

 .the large quantity of lime, which they employ with the muriate 

 ,pf ammonia, to be made red-hot, the retort generally breaks.; 

 and as this does not follow as a matter of course in the London 

 process, I consider it to be really most economical." Had 

 indeed the Edinburgh College directed the lime and the muriate 

 to be made red-hot, as you have here inadvertently stated, the 

 retort would almost infallibly give way, and the balance struck 

 by you might then be a fair one ; the College, however, have 

 ^iven no such directions ; the words are " tandem supponatur 

 ignis sensim augendus donee fundus oUcz ferrece rubescat et quam- 

 diu gas et humor prodierint .^' As thus the heat is to be increased 

 ^Only till the bottom of the sand-pot grows red ; and as the retoEjt 

 Jbas always a quantity of sand interposed ; and further, as much, 

 of the heat is carried off by the gas, the temperature of the mix?- 

 ture is, in every stage very far distant from the point of incan- 

 descence ; indeed the whole ammonia is disengaged long before 

 jtb^ tiemperature could be eley?ited to that point ; and the Phar- 



