OILS AND FATS. 299 



Mr. C. Watt, Sr. ('Newton's Journ.' 1848, and ' Ch. Gaz.' vi.), uses 

 the following method for bleaching dark oils or tallow. To every half 

 ton of oil, take ten pounds of bichromate of potassa. Powder the salt, 

 dissolve it in four pints of hot water, stir, and carefully add fifteen 

 pounds of sulphuric acid, and continue the stirring until complete solu- 

 tion. This mixture is then thoroughly incorporated with the melted 

 fat, previously separated from foreign matters by repose and decantation. 

 The containing vessels should be of wood, and the temperature about 

 130° F. When, after much agitation, the liquid fat assumes a light 

 green colour, the bleaching is completed, four buckets of boiling 

 water are then to be added, the whole stirred for five minutes, and 

 left to repose for several hours, when it will be white and ready for 

 use. 



Mr. Watts, Jr., proposes to recover the chromic acid ad infinitum, and 

 thus render the process very economical, in manner as follows. Transfer 

 the green chrome liquor, after the separation of the fat, to a tub, dilute 

 it with water, and then add thick milk of lime until the sulphuric acid 

 is nearly saturated ; leave to repose, decant the liquor from the sulphate 

 of lime, and carefully add to it another portion of the cream of lime, 

 until the precipitation of all the green oxide and the supernatant liquor 

 is clear and colourless. Drain off this liquor, add fresh water, and, after 

 settling, again decant. Eepeat this washing, then transfer the precipi- 

 tate to a red-hot iron slab, and keep it constantly stirred until it changes 

 to a yellow powder. The chromate of lime thus formed, if decomposed 

 by sulphuric acid in slight excess, yields chromic acid as well suited for 

 bleaching purposes as that from bichromate of potassa. 



A good oil-filter is said to be made of fine sand, charcoal, and 

 gypsum ; the sand to retain substances suspended in it, charcoal to 

 decolourize it, and plaster to remove water. (' Journ. de Chirn Med.' 

 1846.) 



To decolourize raw linseed oil, a solution of two pounds of copperas 

 in two and a half pounds of water is poured into a flask containing two 

 pounds of linseed oil, and exposed to the sun for several weeks, during 

 which it is frequently shaken. The oil is said to be rendered limpid and 

 colourless, and may be drawn off by a siphon, or stoppered funnel. 



Many substitutes have been proposed for the more costly oil for 

 lubricating machinery, but hitherto with only partial success. Mun- 

 kittrick's patent (' Lond Journ.' xxxvi. 98) consists mainly in the addi- 

 tion of caoutchouc to common grease, the former being softened by 

 spirit of turpentine ; but he also uses other ingredients. For example : 

 ten gallons of water being heated, one pound of glue and ten pounds of 

 carbonate of soda are stirred in ; ten gallons of oil or grease are next 

 added, whereby a quasi-soap is formed ; and lastly, four pounds of 

 caoutchouc, softened by turpentine, are incorporated. 



Boudet (' Journ de Pharm.' and ' Lond. Pharm. Journ.' 1850), gives 

 the following as the process by which the French liard, or lubricating 



