After the naphthas have passed re'sid num is forced steam-jaeketed filters Tilled with lame black or fuller': earth; the first portions of the filtrate represent oils, and are followed by successively heavier ones. When the petroleum tit the paraffin the residuum is sometimes placed in the tar still for further distillation, and there the heavy vapors are carried over by the aid of supeilleated steam, the presence of the latter also disso ciation of the oil, which if it owetirred would be followed hy a of viscoosity Of the lubri oil and a decrease in the anniunt of paraf fin obtained. The distillates containing the paraffin arc freed from the latter by the effect of this being to cause a separation of the waxy paraffin scales. The oils thus freed from the paraffin are important lubricants. and under this (lass a number of are known as spin dle oil, engine oil, :Min iner dark oil, winter (lark oil, eylimlcr oil, rulre oil, etc. The residue now left in the tar still is a porous mass of separated carbon, solid decomposition products termed coke, The tar is sometimes used without further distil lation for the manufaeture of vaseline.
of the distillates obtained in the treat ment of mule petroleum contain acid eonstitu euts as well as eompomids which in time impart dark color and unpleasant odor to the distillate.
Raw distillates, when used for pnr poses, also rapidly char the wick and lose their power of drawn upward by capillarity. It is therefore eustomary to purify the various frac tions obtained by 'treatment with sulphuric acid and eaustie soda, before they are marketable. The distillate, which has been first cooled to 60° F.. is with sulphuric. avid in tall cylin tanks of iron lined with sheet lead, and known as about 11:o to 2 per cent. of acid is The acid is then washed out with water. and a 1 per cent, solu tion of caustic soda added, after which a second takes place, followed by The of the various fractions yielded by different oils varies. Alany Pennsylvania oils yield S to 10 percent. 70 to SO per vent. refined oils, 5 to 0 per vent. residuum awl 5 per cent. loss, In the distillation of 100 of crude petroleum there are obtained on the about 76 of oil. 11 of benzine, and naphtha, and 3 of lubricating oil, while the residuum and loss amount to 10