CALCIUM PHOSPHATE AND CALCIUM CARBONATE. 283 



At the still open end was now introduced the other solution — 

 for instance, M/4 sodium carbonate, or M/4 triple sodium phos- 

 phate — and the last border of the cell was then sealed and the slide 

 labeled. All borders were then painted with thick shellac, which 

 was allowed to slightly overlap the wax on to the glass. 



To obtain a series of cells of uniform depth, a sheet of mica 

 four inches by two inches in size was split until the required thick- 

 ness was obtained, equal to that of a number two cover glass. It 

 was cut across with scissors into two-inch strips about two milli- 

 meters wide. One sheet thus prepared will cut into approximately 

 forty or fifty strips. 



Cells filled with warm solutions sometimes showed broken cover 

 glasses on cooling. Also in cells completely filled with solutions 

 a slight amount of expansion due to change of temperature was 

 sufficient to cause leakage by loosening the wax from the slide. 

 And so to provide for permanency of the specimens all cells were 

 so filled as to leave an air space to provide for contraction or ex- 

 pansion without undue strain, and were filled with solutions at 

 room temperature, 20°-2i° C. 



Pure distilled water was used in all experiments, all solutions 

 were filtered to make them perfectly clear, and chemically pure 

 reagents were employed in every case. 



Reaction in Aqueous Solution. 

 Precipitation of Calcium, Phosphate. 



Calcium phosphate was obtained by the interaction of M/10 

 solution of calcium chloride and M/4 solution of triple sodium 

 phosphate in water. This strength of reagent gave plenty of pre- 

 cipitate, without it being so dense as to interfere with proper micro- 

 scopic examination. As the two solutions were of different con- 

 centration, there was a different rate of diffusion on the two sides 

 of the line of contact, with corresponding differences in rate and 

 amount of precipitation. 



Immediately that contact occurs between the two solutions a 

 milky cloud appears, which grows rapidly in size. For a moment, 

 although the cloud is visible to the naked eye, the solution seen 

 microscopically is still clear, but an instant later it becomes vio- 



