122 PUBLIC HEALTH CHEMISTRY 



water. Test with ferric chloride ; a violet coloration, not 

 discharged *by acetic acid, is positive. 



Tartaric Acid. Neutralize with NaOH, add calcium 

 chloride, and shake well : if tartaric is present, a white 

 crystalline precipitate of calcium tartrate falls. To estimate, 

 take 25 c.c, add potassium acetate and alcohol, stand for 

 some hours, stirring occasionally, filter, washing with 

 saturated solution of potassium acid tartrate, dry, and 

 weigh as cream of tartar, KHC 4 H 4 6 , or KHT. 



Poisonous Metals Test for as on page 124. 



VINEGAR. 



Vinegar may be defined as the " product of the alco- 

 holic and acetous fermentation of a vegetable infusion." 

 This definition includes all brewed vinegars, but excludes 

 wood vinegar, made by diluting acetic acid derived from 

 the destructive distillation of wood. The vinegars in 

 common use are : malt, cider, wine, white or distilled, and 

 wood vinegars, and vinegar from starch, glucose, and 

 molasses. The essential constituent is acetic acid, which 

 should not be under 3 per cent in a good vinegar. The 

 other constituents, and their amount, vary with the mode 

 of production : malt vinegar yielding the most, and distilled 

 vinegar the least, extract or total solids. 



Malt Vinegar is made from malted barley, which is first 

 fermented to produce alcohol (by yeast), and the resulting 

 liquid poured over piles of birch twigs, and exposed to the 

 air. The vinegar plant (Mycoderma aceti) grows on the 

 twigs, and converts the alcohol to vinegar, with formation 

 of small quantities of acetic ether, aldehyde, ' and other 

 bodies, which give such vinegar its pleasant odour. 

 Genuine malt vinegar has the following composition : 

 specific gravity at 15-5 F. 1019 ; acetic acid, 5-50 per cent ; 

 extract, 2-50 per cent ; ash, 0-50 per cent ; N, 0-08 per 

 cent ; P 2 5 , 0-08 per cent. It is dextro-rotatory. 



Wine Vinegars are made from grape juice and inferior 

 new wine, and vary in colour from straw to red (malt 

 vinegar is brown). They usually contain 1 per cent of 

 alcohol, 1 per cent of extract, 5 to 6 per cent of acetic acid r 

 not less than 0-25 per cent of ash, and small quantities of 



