600 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



All vegetable and animal oils are compounds of glycerine with 

 fatty acids. When they become old a chemical decomposition 

 takes place, and acid is set free, by which action it is commonly 

 said the oil becomes rancid. This rancid or acid oil will attack 

 the metal of the machinery. For instance, color the brass work 

 all green ; and when this rancid oil is absorbed by rags, and the 

 rags are laying for some time in a heap, it will act on the fibres, 

 produce heat, and finally spontaneous combustion, of which there 

 are daily examples in different localities. 



Petroleum is of another nature; it is not composed of fatty acids; 

 consequently it cannot become rancid. If it could it would have 

 become so long a-io, as it is very old. I have tried to produce 

 such combustion by petroleum, by saturating rags with it, and 

 placing a thermometer in the heap, but have failed to produce the 

 least rise of temperature. There is a petroleum paper manufac- 

 tured intended to be placed between clothes against moths. A 

 box of this paper is perfectly safe; but a box of the same kind of 

 porous paper, soaked in animal oil, in place of petroleum, would be 

 very unsafe, as it surely would become heated, and finally take fire. 



We hope it will not take all the members of the fire depart- 

 ment long to find out that burning petroleum cannot be extin- 

 guished with water. We suppose most of them know this, but 

 perhaps some do not. As water is heavier it goes right to the 

 bottom, and the petroleum floating on the top keeps burning. 

 Some of the water will be changed into steam, from the burning 

 petroleum around, and only cause the fire to spread further. The 

 only way to extinguish burning petroleum is to smother it, by 

 cutting off the supply of air. When this cannot be done it is bet- 

 ter to let it alone than to throw Avater on it, as it anyhow will 

 keep burning till it is all burned up. I have seen in Philadelphia 

 three cases of petroleum fires, where the water poured in a tank 

 containing burning petroleum, caused it to overflow and to increase 

 the damage considerably, as the overflowing burning petroleum 

 set fire to surrounding buildings, fences and sheds, Avhich other- 

 wise would have escaped. In two of these three cases the petro- 

 leum could have been extinguished by covering up the tanks. 



The making of common printer's ink is a very instructive lesson 

 in this respect. It may be made of linseed oil and lampblack. 

 The oil is placed in an iron pot having a cover attached to a long 

 handle. This pot is placed over a brisk fire till the oil boils, and 

 when it becomes thick the fire is communicated to the boiling oil, 



