OILS AND FATS. 371 



is a solution of soap in alcohol. Camphor added to this 

 makes the liquid opodeldoc. Volatile liniment is a sort of 

 soapy mixture made of oil and the volatile alkali ammonia. 

 Equal parts of lime-water and sweet-oil make a soapy mixt- 

 ure which is one of our best applications for a burn. A 

 solution of ammonia in alcohol is very effective in remov- 

 ing grease spots from woolen clothes, because it unites with 

 the grease to form a soap, which readily washes out with 

 the application of a little \vater. 



519. Properties of Fats. Fatty or oily substances have 

 some peculiar properties which fit them for many valuable 

 uses. They spread readily in the pores of substances, and 

 as they are not volatile they answer a valuable purpose in 

 keeping leathern and other articles soft and pliable for a 

 long time. As the fats float upon water, they can be used 

 for excluding air from various substances, thus preserving 

 them from chemical change. Thus a layer of oil is some- 

 times poured over preserved fruits. As the fats are not 

 only insoluble in water, but have a sort of repulsion for it, 

 they are extensively used for preserving substances from 

 being penetrated by water. Shoe-leather is rendered im- 

 pervious to water by greasing. Iron is oiled to protect it 

 from the damp air, and thus keep it from rusting. Tim- 

 bers saturated w r ith oil will be preserved a long time from 

 rotting in the damp earth. 



520. Varnish Oils. All fatty substances on exposure to the air grad- 

 ually absorb oxygen and evolve carbonic acid; and as there is always a cer- 

 tain amount of nitrogenous substance in them, a sort of fermentation occurs, 

 producing acids, and thus making the fats rancid. There are some oils, 

 however, that instead of changing thus gradually in the air, absorb oxygen 

 rapidly and become dry and hard. These drying oils are called varnish 

 oils, because they are so much used in mixing varnish. Linseed-oil is one 

 of the most important of them. It is prepared for varnishing by freeing it 

 from all mucilaginous matter by heating -it with litharge or oxide of lead 

 in it, and mixing it, after this clarifying, with some coloring substance. 



