231 



In order to determine the amount of ammonia, another portion of 

 the powder was introduced into a small tubulated retort, with carbo- 

 nate of soda and water. The neck of the retort was adapted to a 

 small tubulated receiver containing dilute hj'drochloric acid, and 

 having adapted to its tubulure a nitrogen bulb, such as is used in ul- 

 timate organic analysis; this also contained dilute hydrochloric acid. 

 The mixture in the retort was evaporated to dryness ; and at the 

 close of the operation, air was drawn through the apparatus to insure 

 the absorption of the last portion of ammonia. The ammonia thus 

 obtained was estimated by precipitation by chloride of platinum, as 

 in organic analysis, and yielded 0.71 per cent. 



Hence the composition of the concretion is as follows : — 



Phosphoric acid, - - - 32.40 per cent. 



Magnesia, - - - 14.45 



Water, ... - 50.35 



Ammonia, - - - .71 



Insoluble inorganic matter, - .45 



Insoluble organic matter, • - .64 



Hygroscopic moisture, - - 1.00 



100.00 



It will be seen from this, that the amount of ammonia is too small 

 to be considered an essential ingredient of the concretion. Assuming 

 it to exist in the state of double phosphate of ammonia and magnesia 

 with water (NH^O, 2MgO, PO^ + 2H0 + lOHO), and deducting 

 the amount of this salt from the rest (omitting the insoluble matter 

 and hygroscopic moisture), it will be seen that the concretion is com- 

 posed mainly of the phosphate of magnesia and water, according to 

 the following formula 3MgO + 3H0 + 2P05 + 21 aqua, as will 

 be seen from the following comparison : — 



By Experiment. By Calculation. 



Phos. acid, 33.56 2P0^ 33.70 



Magnesia, 14.55 3MgO, 15.20 



Water, 51.89 24Aq. 51.10 



100.00 100.00 



Dr. Coates mentioned some of the symptoms which attended 

 the formation of this concretion, and that it had not been re- 



