CALCIUM PHOSPHATE AND CALCIUM CARBONATE. 285 



For albuminous solutions Merck's powdered soluble egg albumen 

 was employed, water being added to make the approximate normal 

 proportions given by Lillie for fresh albumen in the hen's egg, 

 namely, albumen 12 per cent., water 88 per cent, by weight. 



In 1857 Rainey published the first of a series of papers on the 

 precipitation of carbonate and phosphate of calcium in colloids, 

 using gelatin, albumen, and gum arabic. His best results were 

 obtained with gum arabic, and he pointed out that the solutions of 

 the gum holding the two salts reacting to give the precipitate should 

 be of very different densities, so that diffusion and the consequent 

 reaction would occur slowly and gradually. I have found, how- 

 ever, with albumen and gelatin, that if the reacting salts differ suf- 

 ficiently in concentration, the concentration of the colloidal solution 

 need not differ in order to secure good reactions. And so in many 

 series of experiments 1 per cent, gelatin was used throughout, 

 although in others this concentration was used only with calcium 

 chloride, and a 4 per cent, solution with sodium carbonate or phos- 

 phate. Egg albumen was used always in the same concentration. 



Precipitation of Calcium Phosphate in Colloids. 

 The employment of a colloidal solution seems to have little or 

 no influence on the precipitation of calcium phosphate. The de- 

 posit is quite similar to that in aqueous solutions, being fine, gran- 

 ular, and amorphous (Fig. 36), and aggregating to form thin 

 gelatinous veils and clouds. Results in egg albumen were similar 

 to those in gelatin. These findings are in agreement with the work 

 of Rainey, Harting, Biedermann, and others. 



Precipitation of Calcium Carbonate in Colloids. 



The reaction here is very characteristic. Calcium carbonate 

 formed in the presence of colloids has a tendency to separate out 

 and persist in the form of the spherules mentioned previously, 

 which have been named calcospherites. 



The first effect of the colloid is to very much emphasize and 

 prolong the stage in which the particles are small and show active 

 Brownian movement, apparently by preventing their early fusion 

 into larger masses. In a short time, however, larger particles are 



