in the process of my invention surprisingly i have found that paraffinic hydrocarbons are the preferred solvents any paraffinic hydrocarbon having from about five to about ten carbon atoms or more may be used linear or branched chain species may be used and mixtures of numerous types are satisfactory solvents commercial blends such as naphtha or natural gasoline may be used carbon disulfide cs 2 alone or mixed with paraffinic hydrocarbon solvents are also effective aromatic hydrocarbons such as benzene have not been found to be satisfactory this is an especially unexpected result since such materials are normally considered to be preferred solvents especially for asphaltic petroleum such as is found in tar sands any material which is essentially all gaseous at formation temperature and pressure and which is unreactive with the liquid solvent being used may be used as the carrier gas nitrogen is very suitable for use as the carrier gas in my process air may also be used but precautions must be taken when using a flammable liquid solvent to avoid fire or explosion dangers gaseous paraffinic materials such as methane ethane or propane as well as gaseous olefinic hydrocarbons such as ethylene or propylene may also be used carbon dioxide is another preferred.