In most cases the purification consisted in removing the free fatty acids from rancid oils and fats, the caustic soda forming a soap with the fatty acids, which would either rise as a scum and lift up with it impurities, or fall to the bottom and carry down impurities.
The fatty acids so set free are then more readily attacked by the oxygen of the air, and oxygenated products are formed, which impart to the oils and fats the rancid smell and taste.
Long, and from 1 to 4 lines broad, and have two lateral furrows, a close fracture, a disagreeable rancid taste, and a faint, fishy odour, which last becomes more perceptible when the powder of, the drug is mixed with potash solution.
It does not evaporate or turn rancid, whilst its marked hygroscopic action ensures the moistness and softness of any surface that it covers.
Writing of the Tibetan he states: "As a beverage he drinks, all day long, cupfuls of, hot buttered tea, which is really a soup or broth made by boiling tea-leaves with rancid butter and balls of dough, and adding a little salt, and straining - a decoction which was invariably nasty to our taste, though no doubt it is wholesome; for it is not merely a stimulating hot drink in the cold, but overcomes the danger of drinking unboiled water in a country where the water supply is dangerously polluted."
Whenever he was so fortunate as to have near him a hare that had been kept too long, or a meat pie made with rancid butter, he gorged himself with such violence that his veins swelled and the moisture broke out on his forehead.
Quite distinct is the search for the germs which cause undesirable changes, or " diseases "; and great strides have been made in discovering the bacteria concerned in rendering milk " ropy," butter " oily " and " rancid," &c. Cheese in its numerous forms contains myriads of bacteria, and some of these are now known to be concerned in the various processes of ripening and other changes affecting the product, and although little is known as to the exact part played by any species, practical applications of the discoveries of the decade 1890-1900 have been made, e.g.