01I.S. 145 



upon the sides and bottom of the pan a blackish deposit, 

 which is principally composed of carbon : the process 

 must be repeated after a few days, if the oil have not ac- 

 quired the wished for clearness. Before using the oil, it is 

 necessary that it should be allowed to remain for some 

 time undisturbed. In this operation the mucilage appears 

 to be precipitated and consumed by the acid. Most fixed 

 oils contain some mucilage, and most of them become 

 rancid. 



Most fixed oils have but in a very slight degree the 

 property of drying ; but some of them acquire it by being 

 combined with some metallic oxide, and this greatly in- 

 creases the use of them, as they can in this way be em- 

 ployed as varnishes for covering bodies which it is neces- 

 sary to preserve from air and water ; or as the recipients 

 of colors to be used in painting upon cloth, wood, or metal. 

 The best drying oils are those of flaxseed, nuts, and poppies. 

 Linseed oil will dissolve at boiling temperature ^ of its 

 weight of that oxide of lead known in commerce by the 

 name of litharge. It becomes brown in proportion as the 

 oxide is dissolved : when saturated with the oxide it thick- 

 ens by cooling, and it is necessary to render it liquid by 

 heat at the time of using it. Linseed oil, saturated with the 

 oxide and applied with a brush to any substance, hardens 

 readily and forms a coating impervious by water, and 

 much resembling gum elastic ; linen or silk prepared with 

 it is flexible without being adhesive. 



A cement of this oil prepared with the oxide, and mixed 

 with the refuse or broken fragments of porcelain or of well 

 baked potter's ware, is used with great success in uniting 

 the tiles upon roofs, and in cisterns, and reservoirs. To 

 form this cement the pulverized fragments are thoroughly 

 incorporated with the heated oil, and applied by the trowel 

 whilst in that state. 



When linseed oil is to be used in painting, ^-^ or at the 

 most ^^ part of litharge is sufficient to render it drying. 



In consequence of the numerous purposes to which the 

 fixed oils are applied, the consumption of them is im- 

 mense : they form the basis of the soaps, both* soft and 

 hard, according as they are combined with potash or soda : 

 they are used to fix in the most durable manner upon cot- 

 ton the colors obtained from madder : they are employed 

 to facilitate the operations in all establishments for card- 

 ing and spinning wool. It is by the use of oil that the play 

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