METHODS OF ANALYSIS. 27 



ARSENIC. 



An aliquot portion of the alkaline filtrate (p. 22) is evaporated to 

 dryness. It is then acidified with arsenic-free sulphuric acid and sub- 

 jected to the action of arsenic-free zinc and sulphuric acid in a Marsh- 

 Berzelius apparatus. The mirror obtained is compared with a mirror 

 prepared from an arsenious oxid solution of known strength. The 

 details of this method are given in a former publication. a 



BORIC ACID. 



A part of the alkaline filtrate (p. 22) is evaporated to dryness, treated 

 with 1 or 2 cc of water, and slightly acidified with hydrochloric acid. 

 About 25 cc of absolute alcohol is added, the solution is boiled and 

 filtered, and the operation repeated. The filtrate is made slightly 

 alkaline with sodium hydrate and evaporated to dryness. A very 

 little water is added, the solution slightly acidified with hydrochloric 

 acid, and a strip of turmeric paper placed in the liquid. The whole is 

 evaporated to dryness on the steam bath and the heating continued 

 until the turmeric paper becomes entirely dry. In case boric acid is 

 present the turmeric paper takes on a cherry red color. Boric acid was 

 not determined quantitatively in any of the samples reported. For 

 the sake of completeness a reference is given to a most excellent quan- 

 titative method devised by Gooch. 6 



SILICA. 



In this determination a large quantity of water is evaporated to 

 dryness in platinum, with the occasional addition of small amounts of 

 hydrochloric acid. After all the water has been evaporated to dry- 

 ness the dish and contents are completely dried at 120 C. The residue 

 is taken up with hydrochloric acid and water, heated, and filtered, 

 washing the residue thoroughly with hot water. This process takes 

 out most of the silica. The filtrate is then evaporated to dryness, 

 dried thoroughly at 120 C. , again taken up in hydrochloric acid solu- 

 tion by heatj and filtered. The filtrate is made to a definite volume, 

 aliquot portions of which are used for the determination of iron, alu- 

 minum, manganese, calcium, magnesium, sulphuric acid, potassium, 

 sodium, lithium, and phosphoric acid. The two residifes are trans- 

 ferred to a crucible, burned, and blasted in the ordinary way, and 

 finally weighed as silica/ 



Hay wood and Warner, Arsenic in Papers and Fabrics, U. S. Dept. Agr., Bureau 

 of Chemistry, Bui. 86, p. 25. 



&Amer. Chem. J.,9: 23. 



^This was the procedure as followed in the subjoined analyses. The authors 

 intend, however, in subsequent analyses to determine silica by the difference in 

 weight between the residue and the residue after treatment with hydrofluoric and 

 sulphuric acids. 



