216 PROCEEDINGS OF THE AMERICAN ACADEMY 



This makes a precipitate containing 86.25% of the total Al^Oa, with 

 a composition of 77.10% ALOg and 22.90% SO3. The precipitate 

 at the temperature of boiling has, therefore, lost considerable SO3, 

 while the ratio of the Al^Oa precipitated to the total has not much 

 changed. 



Exp. E^^ . A second variation was made to test the influence of 

 dilution on the equilibrium, since many of the experiments already 

 described indicate that water plays a part in the reaction besides that 

 of a mere solvent. Alum and KOH in the same quantity as in 

 E', E", and E'" were mixed, and the solution made up to 1,000 c.c, 

 instead of 250, making the absolute quantity in unit of volume one 

 fourth what it was in the preceding experiments. Of the filtrate, 

 portions of 100 c.c. were taken, instead of 50, and the quantities of 

 SO3 and AloOa found were multiplied by two in order to make them 

 comparable with the others. The results were : 



AI2O3. SO3. 



I. = .0162 .28570 



II. = .0160 .28578 



Mean = .0161 .28574 



This indicates a precipitate containing 85.05% of total AI2O3, and 

 of composition 66.29% A\Ps and 33.71% SO3. 



Dilution also has tended to diminish SO3 in the precipitate without 

 changing the proportion of AUO3 precipitated. 



Is the equilibriuim a function of time also ? To answer this a 

 mixture was prepared (Exp. E^) at the same time as E', and in pre- 

 cisely the same manner. But instead of filtering at once as in E', the 

 mixture was allowed to stand in a closed flask at the temperature of 

 the room for seven days, and then filtered as in E', and the filtrate 

 analyzed. The result was : 



AI2O3. SO3. 



I. = .0152 .28210 



II. = .0146 .28217 



Mean = .0149 .28214 



This makes a precipitate containing 86.12% of the total Al.Og, and 

 in composition 64.89% AlA and 35.11% SO3, or practically the 

 same as in E'. Here, too, is to be seen the close agreement in 

 quantity of SO3 and the greater variation in AI2O3. 



