Acid Hydrochloric Phosphotungstic

Histidine hydrochloride (2 g.) is suspended in concentrated hydrochloric acid and slowly treated with silver nitrite (3 g.). After removal of excess nitrous acid and silver chloride, the liquid is concentrated to a sirup, which is taken up in alcohol, treated with an excess of alcoholic trimethylamine solution, and kept at 80° for 8 hours. After removal of the alcohol the product is precipitated with phosphotungstic acid. The phosphotungstate is decomposed with barium hydroxide in the usual manner, and the solution of the base thus obtained is strongly concentrated to remove trimethylamine, treated with hydrochloric acid, and the resulting chloride is taken up in alcohol and precipitated with chloroplatinic acid. It is finally converted into the chloroaurate, m.p. 183° with decomposition (14). 

Of the finely divided product, 2 5 grams are mixed to a paste with 10 c.c. of water in a dish, 15-20 c.c. of hydrochloric acid (D 1-19) being added with stirring to obtain a homogeneous mass. After half an hour s rest, the whole is transferred, with addition of hydrochloric add (D 1 125), into a 100 c.c. flask, defecated with 5 c.c. of 4% phosphotungstic acid solution and filtered, the polarisation of the filtrate being determined in a 20 cm. tube in a yellow light instrument. 

Digest about 2-5 g of material with 10 ml of water. Add 20 ml of concentrated hydrochloric acid in small portions at a time the suspension will clear gradually with stirring. Wash into a 100-ml graduated flask with 12 per cent hydrochloric acid, if proteins are present add 5 ml of 4 per cent phosphotungstic acid solution, then dilute to volume with more 12 per cent hydrochloric acid. Shake the mixture well, filter bright (with Dusting-powders the solution does not need filtration) and determine the optical rotation of the solution in a 2-dm tube. 

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