223 



to be submitted to pressure. After this the consistence of the pro- 

 ducts of distillation begins to diminish ; and whilst the temperature 

 of the steam is considerably raised, 21 per cent, of a mixture of solids 

 and liquids distil, the latter predominating especially as the operation 

 proceeds. 



In the last stage of the process the distillate completely changes its 

 character, becoming very dark in colour, of a pitch-like consistence, 

 and exhibiting scarcely an indication of the presence of crystalline 

 matter. When this product, which amounts to about 3 per cent., 

 has passed over, there remains in the still a coke-like mass, which 

 contains a small quantity of earthy impurities. 



Although there is a considerable difference between the specific gra- 

 vities of the first and last fractions of the distillates, all the products 

 of distillation, like the original oil, are lighter than water, and could 

 be separated therefore by means of the well-known apparatus (called 

 a Florentine flask) employed in the distillation of essential oils. 



By exposing the distillates obtained beyond the temperature of 

 145 C. (293 F.) to a freezing mixture, nearly all the crystalline 

 matter solidified, and became removeable by means of filtration and 

 pressure. It was thus ascertained that Rangoon tar contains from 

 10 to 11 per cent, of solid constituents (paraffin). 



Solid Constituents. 



The solid product, when removed from the fluid hydrocarbons, 

 still retains a portion of the latter with much obstinacy ; in order to 

 purify the solid, it has to be subjected to the action of boiling con- 

 centrated sulphuric acid, and to be subsequently washed, first with 

 an alkaline solution, then with water. On redistillation, the paraffin is 

 obtained quite white, but even now it still retains some fluid hydro- 

 carbons which have resisted the action of the sulphuric acid ; the 

 greater part can be removed by pressure between folds of cloth in a 

 powerful hydraulic press and subsequent exposure for some months 

 to the air, in which the fluids gradually disperse. By fractional 

 crystallization from hot alcohol, we have been enabled to separate the 

 solid product into at least two distinct compounds, which appear to 

 have the same per-centage composition, agreeing either with C n H n or 

 C n H n+1 , but which differ from each other in their physical properties. 

 By the action first of sulphuric acid saturated with anhydrous acid, 



T2 



