TABLES FOR REFERENCE. 



263 



Crystal Systems. 



Isotonic Coefficient. 



Two solutions of equal power to take up water are said by 

 De Vries to be in isotonic concentration. He terms a num- 

 ber showing the water-absorbing power of a given solution, 

 as compared with that of a solution of saltpeter of equal 

 strength taken as a standard, its isotonic coefficient. For con- 

 venience, the coefficient assigned to saltpeter is 3. 



De Vries finds that compounds fall into six groups whose 

 coefficients are approximately whole numbers, as follows : ' 

 I. Organic compounds not containing metals, and free 

 acids; e.g., Cane-sugar, tartaric acid, citric acid, 

 etc. 2. 



II. Salts of alkaline earths with one acid group in the 

 molecule ; e.g., Magnesium sulphate and malate. 2. 

 III. Salts of alkaline earths with two acid groups in the 

 molecule ; e.g., Magnesium chloride and citrate, cal- 

 cium chloride. 4- 



