Detection of Adulterations. 83 



solution of phosphate and nitrate of barytes. Precipitate the phos- 

 phate by pure ammonia, filter, and add to thclluid, carbonate of am- 

 monia, by which we shall precipitate carbonate of barytes, 100 grains 

 of which indicate 144 grains of crytallized carbonate of soda.* 



Soda. — The carbonates of soda met with in commerce are very 

 variable in their composition ; some of the fine crystals being nearly 

 pure, while the coarser preparations are largely mixed with a variety 

 of substances* The mode of examination usually applied to the 

 carbonates of this alkali and of potash, are founded on their power 

 to neutralize acids. As, however, the process is described in the 

 popular w r orks on chemistry, we shall not repeat it in the present in- 

 stance, but will proceed to mention some impurities which are liable 

 to influence the neutralizing power of the carbonate, and therefore 

 to interfere with the accuracy of the results obtained by the usual 

 examination. In testing the solubility of specimens made from the 

 sulphate of soda, it is better to dissolve them in cold than in hot water ; 

 since the latter dissolves more readily the sulphuret of lime, which 

 then reacts upon the carbonate of soda, converting it into a hydro- 



t 



The presence of the 



sulphite and of the hydrosulphuret also tends to create error, as they 

 neutralize a portion of the acid used as a test, and thus raise the ap- 

 parent neutralizing power of the carbonate beyond its real power. 

 This disadvantage is avoided by mixing the carbonate with one fifth 

 or one third its weight of chlorate of potash, and exposing the mass 

 to a red heat, in a platina crucible. The sulphuret and sulphite are 

 thus converted to sulphates, which cannot combine with any portion 

 of the acid used in the examination. If the specimen to be exam- 

 ined be very impure, and contain much insoluble matter, it will be 

 best to dissolve all the soluble portion, add the chlorate to the solu- 

 tion, evaporate to dryness, and then proceed as before. 



When, on pouring sulphuric acid into a solution of any of the car- 

 bonates of commerce, there is a simultaneous disengagement of sul- 

 phur and sulphurous acid, the presence of the hyposulphite of soda 

 is indicated. This salt, however, does not affect the neutralizing pow- 

 er of the specimen in which it exists, since its base cannot combine 

 w ith any acid, without separating from that with which it is already 



* The quantity of water of crystallization varic - somewhat according to the few 

 perature at which the crytals are formed. 



t We are not satisfied ts to the nature of this solution. 



