It does not evaporate or turn rancid, whilst its marked hygroscopic action ensures the moistness and softness of any surface that it covers.
Large quantities of butter, generally rancid, are made from the milk of cows, goats and sheep. In the Leka province small black pigs are bred in considerable numbers.
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."
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.
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.