CONCLUSIONS. 57 



Three grades have been suggested by this bureau for gum spirits, 1 

 and there appears to be no reason why wood turpentines should not 

 be graded in the same way and comply witli the same specifications. 

 [These specifications are: 



Standard or No. 1 turpentine should have a specific gravity at 20 C. of from 0.862 

 [to 0.870; a refractive index at 20 C. of from 1.468 to 1.476; 95 per cent should distill 

 ielow 170 C., and a layer of not less than 200 mm should be required to equal in color 

 [the Lovibond yellow glass No. 1. On polymerization with 38 normal sulphuric acid 

 the residue should not exceed 1 per cent, should be reddish in color and viscous, and 

 its refractive index at 20 C. should be from 1.500 to 1.520. An unadulterated tur- 

 |pentiiie which does not agree with these requirements may properly be regarded as 

 >t of standard or No. 1 quality. 

 Second quality or No. 2 turpentine should have a specific gravity at 20 C. of from 

 .862 to 0.875; a refractive index at 20 C. of from 1.468 to 1.480; 90 per cent should 

 .istill below 170 C. and a depth of not less than 100 mm should be required to equal 

 [the Lovibond yellow glass No. 1. The polymerization residue must not exceed 1 per 

 ;nt and must have a refractive index of not less than 1.50. 



Third quality or No. 3 turpentine should have a specific gravity at 20 C. of from 



1.865 to 0.880; a refractive index at 20 C. of from 1.468 to 1.485; 60 per cent should 



istill below 170 C. and a depth of not less than 50 mm should be required to equal 



.e Lovibond yellow glass No. 1. The polymerization residue must not exceed 1 per 



mt and must have a refractive index of not less than 1.500. 



Wood turpentine that complies with the specifications for No. 1 

 md No. 2 turpentines will have but little objectionable odor, and it 

 is believed will meet all reasonable technical requirements for paint 

 md varnish thinners, except possibly those for varnishes of the 

 dghest grade. 



TALUE OF WOOD TURPENTINES AS PAINT AND VARNISH THINNERS. 



The experimental work which has been done and the information 

 that has been collected leave no doubt that wood turpentine, both 

 destructive and steam distilled, can, by careful refining, be made to 

 correspond closely with gum spirits in all those properties by which 

 the suitability of turpentine, as a paint and varnish thinner, is judged. 

 The wood turpentine that contains no products of destructive distil- 

 lation and is free from heavy oils differs very slightly in odor from 

 gum spirits, and but little, if any, objection can be raised to the 

 technical use of well-refined wood turpentine on this account. It 

 may be used in well- ventilated places without serious inconvenience 

 to the workmen. Well-refined wood turpentine is a suitable paint 

 and varnish material, except possibly for the highest grade varnishes; 

 and it may be emplo} r ed for these purposes without detriment to the 

 paint or varnish. 



1 U. S. Dept. Agr., Bureau of Chemistry Bui. 135. 



