95 



particular pavement laid in 1895, the surface of the aggregate was 44 

 square feet per lb. of material, whereas in a later one the surface was 

 iucreased to GO square feet per lb. The former pavement was 

 unsatisfactory, and the latter was excellent. 



Naturally occurring colloidal suspensions are found in Trhiidad, 

 where the asphalt contains 25 per cent, of finely divided mineral 

 matter, but artificial mixtures of bitumen and dispersed clays can be 

 made which may contain as much as 60 per cent, of mineral. The 

 various asphalts (natural and artificial) possess different powers of 

 retaining the disperse phase. Broadly speaking, asphaltic residues 

 from crude oils are inferior in this respect to the natural bitumens. 



Mixhtres of 67 per cent. Bitumen and 33 per cent. Clay {introduced while 

 wet) and maintained at 325° F. for 24 hours. 



The temperature 325° F. is that at which is formed the film of 

 bitumen which covers the mineral aggregate of a sheet asphalt 

 pavement. It is striking that the Trinidad residual is so thoroughly 

 differentiated from all the others, confirming the opinion based upon 

 service tests in regard to the unique character of this material. 



Although m actual refining operations the adsorptive properties 

 of the materials described above have mainly been directed towards 

 the removal of colour, yet considerable success has been achieved 

 in connection with the equal important problem of desulphurisation. 

 It by no means follows that an adsorbent is equally effective in 

 removing colouring matters and sulphur derivatives. Usually this 

 is not the case, and each material must be tested for its specific 

 purpose. So far as the writer's experience goes, the sulphur compounds 

 present in the fighter distillates are more readily adsorbed than those 

 in the higher boiling fractions, although it is possible that in the 

 latter case there is preferential adsorption of other substances, e.g., 

 unsaturated hydrocarbons. Whilst for example, floridin will desul- 

 phurise benzine quite readily, it has little effect on the sulphur 

 compounds which occur in the lubricating oils derived from the same 

 crude petroleum. 



An interesting application of adsorption is to be seen in the method 

 patented by Hall Motor Fuel, Ltd., for the purification of cracked 



