TRANSACTIONS OP THE SECTIONS. 63 



Ohservations on the Co?istitution of the Commercial Carbonate of Am- 

 monia. By Mr. Scanlan. 



Having occasion some months ago to make a quantity of the " So- 

 lution of Sesquicarbonate of Ammonia," of the London Pharmacopoeia, 

 the author found, (without knowing that Dr. Dalton had done so be- 

 fore,) by pouring successively small portions of pure water on large 

 quantities of the salt, that saturated solutions were obtained, success- 

 ively decreasing in specific gravity, and smelling less and less of 

 ammonia, till all the salt was dissolved. He agrees with Dr. Dalton 

 in opinion, that the commercial carbonate of ammonia is not a homo- 

 geneous salt, not a sesquicarbonate of ammonia, but a mixture of car- 

 bonate and bicarbonate, of which the former is first dissolved by the 

 water. The irregular masses of salt which remain still retain, almost 

 exactly, their original form and dimensions — they are, in point of fact, 

 skeletons of the original mass, but consist solely of a congeries of cry- 

 stals of bicarbonate of ammonia, from the interstices of which carbo- 

 nate of ammonia has been removed by the solvent power of the water, 

 if we do not proceed so far as to dissolve all. What takes place here, 

 may be likened, in some measure, to the case in which the gelatin is 

 removed from bone by water, leaving the phosphate of lime. Inde- 

 pendently of showing the true nature of the salt, this is of some im- 

 portance, as it affords us a very ready mode of preparing bicarbonate 

 of ammonia without the waste, which occurs by exposure of the com- 

 mercial salt in powder to the air, or without the trouble of transmitting 

 a current of carbonic acid gas through its solution, as directed by the 

 Dublin Pharmacopoeia. Indeed, the latter method is both troublesome 

 and wasteful, for it is difficult to evaporate a solution of bicarbonate of 

 ammonia without decomposition. Mr. Scanlan has found that water at 

 90° or 100° decomposes bicarbonate of ammonia, setting carbonic acid 

 at liberty. 



On the Blackening of Nitrate of Silver by Light. By Mr. Scanlan. 



Nitrate of silver was recommended many years ago, by Dr. John 

 Davy, as a test of the presence of organic matter in distilled waters. 

 He showed, that if nitrate of silver in solution be added to perfectly 

 pure water, it is not altered by exposure to direct sunshine ; but if the 

 water contain a trace of organic matter, it will become blackened. 

 Mr. Fergusson, some years ago, when he had the management of the 

 chemical laboratory belonging to the Dublin Apothecaries Company, 

 informed Mr. Scanlan, that perfectly pure nitrate of silver is not 

 blackened by long exposure to direct sunlight, but it is believed that 

 he never gave further publicity to this fact than mentioning it to his 

 chemical friends in Dublin at the time. In consequence of some 

 observations upon the blackening of this salt, made by Dr. Aldridge, 

 of Dublin, in his review of Mr. Phillips's translation of the London 

 Pharmacopoeia, Mr. Scanlan was led to make the following experiment 

 upon the subject : — He took two cylinders of perfectly pure fused 



