FOODS 99 



the flour floats to the top and any mineral matter sinks to 

 the bottom. Draw off, dry, weigh, and examine micro- 

 scopically. Any soluble matter can be dissolved and tested 

 for alum, while the insoluble can be tested for CaS0 4 , 

 BaSO 4 , and CaCO 3 . To test for alum : add NaOH, white 

 precipitate solution in excess of NaOH, but re-precipitated 

 on adding AmCl. The sulphuric acid present in alum is pre- 

 cipitated by barium chloride ; precipitate insoluble in HC1. 



Bleaching of Flour. Chiefly with nitrogen peroxide 

 (N0 2 ), produced by the action of HN0 3 on FeS0 4 , or 

 combustion of NH 3 in air, or by electric sparks. The 

 NO 2 with the moisture in the flour forms nitric and nitrous 

 acids, the latter of which is readily demonstrated in a io 

 per cent watery extract by the Ilosvay method (page 48) . 

 (i to 3 parts as N per million). (See Hamill and Monier- 

 Williams, Journal of Hygiene, vol. xi, No. 2, July, 191 1). 



Alum. Make 10 grm. of flour into a paste with 10 c.c. 

 of water. Add 1 c.c. of each of two solutions, namely, 

 (1) Fresh tincture of logwood, and (2) Saturated solution 

 of ammonium carbonate. Mix well with a glass rod. If 

 the flour is free from alum, the mixture is a pinkish colour 

 fading to a dirty brown. If alum is present, the pink 

 changes to a lavender tint or even to a blue. In such a 

 case the sample should be put in the water-oven for two 

 hours to make sure that the colour is permanent. 



Adulterations. Those mentioned under cereals; water; 

 " improvers " ; also foreign seeds. One of these, the purple 

 cow- wheat (Melampyrum arvense), is not injurious, but 

 gives bread from the flour a smoky- violet or bJuish-violet 

 tint. Two others, the corn-cockle (Agrostemma githago) 

 and darnel seeds [Lolium temulentum) possess toxic powers. 

 The corn-cockle is detected by its appearance as large 

 black seeds, while the darnel seeds are detected by the 

 repulsive taste they give to the flour and the greenish 

 colour produced on the addition of alcohol (pure flour 

 gives a straw-coloured solution with a more or less agree- 

 able taste). Darnel seeds do not affect the colour of the 

 bread, but produce in those eating it, vertigo, hallucina- 

 tions, delirium, and narcosis. 



Bread is made by kneading wheat flour with water, the 

 coherence of the dough being due to the moist glutin 



