174 PREPARATION OF FARINA AND SUGAR. [ VII. 



ebullition, diluted with water, and then treated with a few 

 drops of nitrate of cobalt solution, yields a bluish-violet pre- 

 cipitate, which after some time has a greenish color. A con- 

 centrated solution of starch-sugar, similarly treated, yields a 

 dirty, light-brown precipitate ; or, if dilute, remains clear. A 

 very small quantity of starch-sugar contained in cane-sugar 

 prevents the violet precipitate by nitrate of cobalt. 



Chevallier tests the presence of starch-sugar in cane-sugar 

 by warming the solution with caustic potassa, whereby a greater 

 or less quantity of the former produces a red or yellow color- 

 ing. According to Cotterau, all the caustic alkalies, including 

 ammonia, produce this effect, — even their carbonates, but not 

 their bicarbonates, — and hence he proposes starch-sugar as a 

 test for the presence of neutral. 



Maumene (L'Institut, No. 846, and Silliman's Journ. 1850) 

 proposes bichloride of tin as a reagent for detecting the pre- 

 sence of sugar in urine ; the test-cloth is made of white merino, 

 saturated with diluted tin solution, drained and dried in a 

 water-bath. This cloth, when spotted with urine and held 

 over a heated coal, turns black in the moistened places if 

 sugar is present ; whereas the stain of ordinary urine is not 

 darkened. The reaction is due to the dehydration of the 

 sugar, highly carbonated caramel being formed. 



The author suggests the possibility of forming a useful 

 brown pigment by the above reaction. 



Quantitative Test for Cane-sugar. — Peligot's method de- 

 pends upon the definite constitution of sugar-lime, its greater 

 solubility in water than lime alone, and the unalterability of 

 this solution by heat. Soubeiran had found that sugar-lime 

 consisted of 3 eq. lime to 2 eq. sugar, i. e. 84 pts. lime to 

 342 pts. sugar, or 1 : 4. 10 grm. sugar are dissolved in 75 

 cub. centimetres water, ground up with 10 grm. slacked lime, 

 filtered, and again filtered through the lime. 10 cub. cent, 

 of the filtrate, diluted with 2-3 decilitres water, and tinctured 

 with a little litmus, are carefully neutralized by a measured 

 volume of dilute sulphuric acid (21 grm. oil of vitriol in 1 litre 

 vrater), and the quantity of acid used noted. It gives the 



