The Phosphates of America. 145 



over a small Bunsen flame for ten minutes, and is then brought to a 

 white heat by means of the blast. After being kept at this high 

 temperature for five minutes the flame is removed, the crucible 

 is covered ; placed in the desiccator ; and allowed to become 

 quite cold. It is then weighed, and the difference between the 

 present weight and that of the residue from the moisture deter- 

 mination -f- 2 represents the " loss on ignition " in one gramme of the 

 material. 



The total of this loss on ignition includes water of combination, 

 organic matter, and carbonic anhydride, and as the latter is to 

 be determined separately, its weight when found must be deducted 

 from this total. 



Carbonic Anhydride (CO 2 ). 



This is one of the most essential of the determinations, and 

 should be made in every sample destined for factory use. There 

 are numerous excellent methods of performing it, but the two 

 most commonly used in our laboratory are those of Scheibler and 

 Schrotter. The first-named is based upon the principle that the 

 quantity of carbonic anhydride contained in pure chalk can be used 

 as a measure of the quantity of that salt itself. Instead of estimat- 

 ing the carbonic-acid gas by weight, therefore, this method allows 

 of its estimation by volume, and when skilfully handled it yields 

 very rapid and very accurate results. The second is a far simpler, 

 and in our experience equally expeditious, method, and our students 

 consequently take more readily to it than to the other. It only re- 

 quires ordinary care in its manipulation to give perfect satisfac- 

 tion. 



A mere glance at the figure w r ill suffice to show that the appa- 

 ratus is made of blown glass, and that its principle depends upon 

 the loss of weight which occurs in a carbonate when its carbonic- 

 acid gas is expelled. 



Two grammes of the original substance are accurately weighed 

 and introduced into A. The tube B is now filled with fifty per 

 cent, hydrochloric acid and the tube C about a quarter filled with 

 concentrated sulphuric acid. All the stop-cocks have meantime 

 been kept closed, and the apparatus is now brought upon the scale 

 and very accurately weighed. The weight being noted in the 

 agenda it is withdrawn from the scale, the stop-cock on tube B is 

 gradually opened and the hydrochloric acid thus allowed to come 

 into contact with the phosphate. When all the acid is in, the tap 



