96 



spirit. This material, as is well known, contains a considerable 

 proportion of highly unsaturated hydrocarbons — olefines and diolefines 

 — to the presence of which it owes its characteristic odour and its 

 objectionable propensity towards resinification or " gumming." 

 Although the reactive hydrocarbons can be removed by the agency 

 of strong sulphuric acid, the operation is attended by serious loss, 

 but by iitihsing the adsorbent capacity of floridin, the diolefines present 

 are polymerised to high boiUng products and a spirit free from 

 objection is produced. The refining operation is best carried out 

 with the spirit in the vapour state, under these conditions adsorption 

 is followed by condensation and/or polymerisation. 



Incidentally the sulphur derivatives present in many_^benzines 

 and kerosenes may be removed in a precisely similar manner. 



The problem of the breaking of persistent emulsions in refining 

 operations is obviously one for treatment by the application of coUoid 

 chemistry. The soda wash which is employed to remove the traces 

 of sulphuric acid in the refining of lubricating oils is a common source 

 of this trouble and in some cases a practically permanent emulsion 

 is formed. The sodium salts of naphthenic and sulphonated naphthenic 

 acids are notable emulsifying agents and it is possible that hereinlies 

 the cause of what is sometimes a serious diflBcuit3^ It is interesting to 

 remember that sodium naphthenates are used very extensively as soap. 



A recent patent by Southcombe and Wells brings out the novel 

 point that a small amount (1 per cent.) of free fatty acid added to a 

 mineral lubricating oil, not only replaces the usual blending fatty 

 oil, but according as its niolecular weight is lo^^' or high, yields a 

 non- emulsifying or an emulsifjdug oil. It appears that the addition 

 of the free fatty acid appreciably lowers the interfacial tension 

 between the lubricating oil and the bearing. 



Petroleum jelly or " vaseline " appears to be an emulsion of soft 

 paraffins dispersed in heavy oUs. The viscosity increases gradually with 

 decreasing temperature until the gel state is attained, without, however, 

 any separation of crystalline wax, but on being distUled, wax appears 

 in the distillate. Various artificial jeUies are on this market, being com- 

 pounded of soft wax and heavy oil, these, on the contrary, are inclined 

 to deposit crystalline matter on being cooled, and do not possess 

 the salve-like nature of the natural product.* An apt comparison 

 is in the different appearance of ice cream made with and without 

 the addition of gelatine and in both cases — vaseUne and ice cream — 

 the presence of a protective coUoid may be the explanation. 



A pecuUar illustration of the coagulation of a colloidal solution 

 is seen in the action of flowers of sulphur on the jeUow liqvud which 

 is produced by treatment of sulphur-containing distillates with 

 sodium plumbite. There is a rapid flocculatiojn and a dark brown 

 precipitate appears. 



* By this is meant the inaterial which is obtained from a suitable crude oil 

 by distilling off the lighter compounds and decoloriBing the residue (usually by 

 filtration through fuller's earth). 



