90 



BTLLETIX 1036, TJ. S. DEPAETMEXT OF AGRICnLTUEE. 



the method in which ghacial acetic acid was employed, that in which 

 benzol was used as a solvent gave the highest results. All the 

 solvents except aniline gave higher results \\-ith longer digestions. 

 With the use of aniline the insoluble matter decreased from 5 per 

 cent after one-half hour to 4.6 per cent after 144 hours, and this was 

 the lowest result obtained. 



Weiss further showed that the insoluble residue, after digestion with 

 chloroform, contained noticeable amounts of chlorine. Sulphur was 

 also found in the residue resulting from the digestion with carbon 

 bisulphide. 



Monroe and Broderson (^J) investigated the action of benzol and 

 chloroform on the free-carbon content of three classes of tar. The 

 results of their work are plotted in figure 42. Here again they found 



that benzol yields a greater insoluble 

 residue than does chloroform, not- 

 withstanding the fact that consid- 

 erable quantities of clilorine were 

 found in the residue. This amount 

 increased with the time of digestion. 

 From the above it is apparent 

 that, if this test is designed to deter- 

 mine the free carbon in tars, a di- 

 gestion with aniline would give the 

 more nearly correct result. But if 

 a purely empirical determination is 

 all that is desired, then any one of 

 ^ the solvents is satisfactorv provided 



iiG. 42. — Chanee in apparent free carbon content i i • ' i i i 



oftars with changein time of digestion. that the tcst IS made Standard and 



the conditions of the test are defined 

 and rigidly adhered to. 



The method adopted as standard 

 by the American Society for Testing Materials, the American Rail- 

 way Engineering Association, and the American Wood Preservers' 

 Association is as follows : 



Apparatus. — (A ) Extractor may be of the form shown in figure 43 or similar form 

 in which the oil is subjected to direct washing by the boiling \apors of the solvent. 



{B) Filtering mediiim may be either two thicknesses of S. and S. No. 575 or ^"hat- 

 man No. 5 hardened filter paper, 15 cm. in diameter, arranged in cup shape by folding 

 symmetrically; or alundujn thimbles, flat bottom, 30X80 RA 98. If filter papers 

 are used they shall be soaked in benzol prior to using to remove grease, dried in a 

 steam oven, and kept in a desiccator until ready to be used. The filter-paper cup 

 may be suspended in the extractor flask by a wire basket hung from two small hooks 

 on the under suriace of the metal cover of the flask. 



If the alundum thimble is used it may be supported by making two perforations in 

 the top of the thimble and suspending from the cover by German silver or platinum 

 wires. 



■r^ 



jI ^ -p 



.'rf — 



2s ^^^J^ — r 



-I 



* 2 



|3 



2 



40 SO 60 

 TIBE-HOURS 



Numbers represent tars No. 1, 2, and 3. 

 X. Extractionsmade with benzol. 

 O. Extractionsmade with chloroform. 



