48 GENERAL DISCUSSION OF CLAYS. 



oxalate precipitate Is concentrated to about one hund- 

 red cubic centimetres, cooled, and the magnesium pre- 

 cipitated by means of hydrogen disodium phosphate 

 in a strongly alkaline solution, made so by adding ten 

 cubic centimetres of ammonium hydroxide (0.90 sp. 

 gr.). The magnesium ammonium phosphate, iafter 

 standing over night, is caught upon an ashless filter, 

 washed with water containing at least five per cent, 

 ammonium hydroxide, burned and weighed as mag- 

 nesium pyrophosphate. 



The insoluble residue is determined by dige-'ting 

 two grams of clay with twenty cubic centiments of 

 dilute sulphuric acid for six or eight hours on a sand- 

 bath, the excess of acid being finally driven off. One 

 cubic centimetre of concentrated hydrochloride acid 

 is now added and boiling water. The insoluble por- 

 tion is filtered off, and after being thoroughly washed 

 with boiling water is digested in fifteen cubic centi- 

 metres of boiling sodium hydroxide of ten per cent, 

 strenth. Twenty-five cubic centimetres of hot water 

 are added and the solution filtered through the same 

 filter paper, the residue being washed five or six times 

 with boiling water. The residue is now treated with 

 hydrochloric acid in the same manner and washed up- 

 on the filter paper, and free from hydrochlOxC acid, 

 is burned and weighed as insoluble residue. 



A portion of this is treated as the original clay for 

 silica, aluminium oxide and iron oxide. Another por- 

 tion is used for the determination of the alkalies in 

 the insoluble residue. 



Titanic Oxide — One-half gram of clay is fused with 

 five grams potassium bi sulphate and one gram sodium 

 fluoride in a spacious platinum crucible. The melt is 

 dissolved in five per cent, sulphuric acid. Hydrogen 

 dioxide is added to an aliquot part and the tint com- 



