180 THE SECRETIONS: 



entirely of earthy phosphates, occupied, when it had entirely 

 settled, one third of the volume of the fluid. I received from 

 a physician of this city, a portion of dried urinary sediment 

 which consisted almost entirely of pure earthy phosphates. 

 This fragment bore evident traces of the form of the glass in 

 which the urine had been kept, and it was of the extraordinary- 

 thickness of nearly an inch and a half. Earthy-phosphate sedi- 

 ments are seldom perfectly pure ; their colour is white, gray, 

 yellow, or reddish. White and gray sediments consist princi- 

 pally of earthy phosphates and mucus; yellow and reddish sedi- 

 ments contain a greater or less admixture with urates. 



That the sediment is composed of earthy phosphates we are 

 assured by the following chemical facts. The urine from which 

 it is precipitated is neutral, or more commonly alkaline; the 

 sediment does not dissolve on the application of heat, like the 

 urates ; it is, however, readily dissolved by the addition of an 

 acid (hydrochloric, nitric, or acetic,) to the urine ; a property 

 which is not enjoyed by sediments of the urates, of mucus, or 

 of pus. If the sediment contain so large a proportion of urates 

 and mucus that the addition of an acid does not produce any 

 obvious degree of clearing, the acidulated urine must be gently 

 warmed and filtered from the insoluble constituents. Upon the 

 addition of free ammonia to the clear, filtered fluid, the earthy 

 phosphates will be precipitated. 



The nature of the sediments may be still more quickly ascer- 

 tained by the microscope. If the sediment consists of earthy 

 phosphates, we observe the beautiful crystals of ammoniaco- 

 magnesian phosphate depicted in fig. 27, and also amorphous 

 masses of phosphate of lime, fig. 26. Upon the addition of a 

 minute quantity of free acid to the objects on the field of the 

 microscope the crystals and amorphous masses immediately dis- 

 appear, and at the same time numerous air-bubbles are liberated. 

 If the earthy phosphates have been dissolved by a little acidu- 

 lated water from the urates and mucus or pus, with which they 

 were associated, and are then precipitated from the filtered 

 solution by free ammonia, the precipitate exhibits other forms 

 under the microscope. 



I have represented these forms, which seem to vary according 

 to circumstances, in fig. 30. Fig. 30 a exhibits the different 

 forms under which the ammoniaco-magnesian phosphate is pre- 



