772 SHALES AND MINERAL OILS 



The merit of the common German lamp, -whose introduction rendered these oils 

 capable of domestic use, is in the introduction of so much air as thoroughly to con- 

 sume the very great amount of carbon disengaged in their combustion. The sp. gr. 830 

 appears to indicate the highest number, in weight of the oil, capable of being con- 

 sumed -with comfort in such lamps. But inventors, such as Doty and Silber, have 

 striven -with some success to utilise the intermediate oils up to 888, the recognised 

 standard of superior mineral machinery-oil. All such oils possess higher luminosity 

 and safety. The varied lamps for these purposes differ from the one used for common 

 burning oil in admitting more air, so as to counteract the soot caused by the greater 

 amount of carbon disengaged ; and in adapting the shape of the lamp and the wicks, 

 so as to cause those heavier oils easily to ascend them. The refiner is content to give 

 all such higher oils a lemon-straw colour. So, in a very general way, it may be said 

 that specific gravity and flash-point are the distinguishing features of the different 

 products of destructive distillation at a low red heat. The relative figures of the 

 hydrometer only may be taken as distinctive approximations of these different oils. 



Lubricating Oils. Dr. Wallace reports that in nine experiments on lubricating oils 

 there was a varying specific gravity from 881 to 900 ; and the flash-points ran from 

 293 to 388 Fahr. In seven experiments the flash-point was over 300 Fahr. As 

 with the lighter oils, specific gravity is no a priori test of safety. The highest specific 

 gravity amongst the samples 900 had the comparatively low flash-point 309 : another 

 sample 20 in sp. gr. below this was only minus 1 Fahr. in flash-point; whilst 

 another sample, 10 in sp. gr., below the first was 19 Fahr. in flash-point above it. 

 The following are the specific gravities and flash-points of some well-known fatty 

 oils : 



S. G. P.-P. 

 Fahr. 



Whale oil (best) 923 492 



Cloth oil (wool oil) . . . .917 320 



Olive oil 917 420 



(genuine) .... 920 500 



Rapeseed oil 913 440 



Lard oil .914 560 



Tallow oil 915 490 



Mr. Gellatley's experiments on cotton-waste steeped in various oils ('British Asso- 

 ciation Report, 1872 ') appear to show that where a liability to high heats exists in 

 using machines, mineral oils are safer than the older ones. Manufacturers are pain- 

 fully aware of the liability to spontaneous ignition of cotton-waste which has been 

 soaked with such a rapid oxidiser as linseed oil. Again, at a particular stage of 

 calico-printing with Turkey-red, the batch is saturated with olive oil ; and it cannot 

 bo allowed to lie for more than an hour without danger of spontaneous ignition. 



For a discussion of the firing-points of burning oils, and their relative dangers, see 

 NAPHTHA. 



Preparation of Crude Oil. When beginning the manufacture near Bathgate, Mr. 

 Young used Torbanehill mineral as his raw material, though he was previously awaro 

 that any cannel would equally have served hia purpose. But by the competition of gas- 

 makers they have withdrawn all such bituminous substances from the oil-maker's 

 market (see PARAFFIN) ; and even shale is now subject to a similar rival clement. Shale- 

 is distilled in either horizontal or vertical retorts of cast iron. The charge of the 

 horizontal retort is made in either the twelve or twenty-four hours, and varies from 

 6 to 12 cwts. Vertical retorts hold about a ton of shale, but are continuous; the 

 charge is fed through a hopper at the top, and drawn out at the foot when exhausted, 

 above a tray filled with water. Machinery has been introduced in some Scotch 

 works for filling and discharging the retorts. With horizontal retorts it is not re- 

 quisite to break the shale into small pieces the size of a hen's egg as specified by 

 Young. -A Carr's stone-breaker usually effects this for the vertical retorts. Scotch 



