IIG. Mr. W. B. Hardy. On the Conditions vjhich 



Mastic, Dialysed, Neutral, Electro-negative. 



Temperature 16°, Concentration of fJoagulating Salts, 1 gramme-mol. 



in 50,000. 



Coagulates at once. No coagulation. 



Al2(S04)3 K2SO4 



CUSO4 Na2S04 

 CuCl2 NaCl 



Cd(N03)2 



MgS04 

 BaCl2 



Ferric Hydrate, Dialysed, Neutral, Electro-positive. 

 Temperature 16°. Coagulating Salt 1 gramme-mol. in 100,000. 



Coagulates at once. Does not coagulate. 



Al2(S04)3 . CuCl2 



CUSO4 Cd(N03)2 

 MgS04 NaCl 

 K2SO4 BaCl2 

 Na2S04 



Gold, Dialysed for fourteen days against Distilled Water, very faintly 

 Acid. Electro-negative. 



Temperature 16°. Coagulating Salt 1 gramme-mol. in 200,000. 



Ked changes to blue* 



instantly in— No change. 



Al2(S04)3 NaCl 

 CUSO4 Na2S04 

 CUCI2 K2SO4 



Cd(N03)2 



MgS04 

 BaCl2 



Only one comment on these experiments is needed. Solutions of 

 Al2(S04)3, Cd(N03)2, CuCl2, and CUSO4, are acid to litmus, while MgS04, 

 and BaCl2 are neutral to litmus, but acid to nhenol phthalein. This 

 acidity has a disturbing action in some cases — the system acts not 

 only as a neutral salt, but also as a free acid. Thus the hydrosol of 

 proteid when brought very near to the point of precipitation by 

 dialysis is more sensitive to the more acid than to the less acid salts of 

 the bivalent metals. The effect of the acid or basic reaction of the 



* The relation of the colours of hydrosols of gold to the size of the particles has 

 been investigated by Stoeckl and Yanino ('Zeits. f. phys. Chem.,' vol. 30, 1899, p. 98). 

 The change from red to blue indicates an increase in the size of the particles. 



