34 



BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 



perature. It frequently happens, however, that creosotes are 

 analyzed in laboratories equipped for that purpose only; for such an 

 equipment a special steam-bath or oven may be made by any tin- 

 smith at small cost. It is essential that the chamber be of sufficient 

 size to contain the Babcock bottle completely. Otherwise the exact 

 dimensions of the steam bath are unimportant. The 37/N sulphuric 

 acid is prepared by mixing fuming sulphuric acid mth enough 

 ordinary sulphuric acid so that the finished mixture will contain 

 80.1 per cent SO3. Fuming sulphuric acid may be purchased in 

 different concentrations, and there are two methods in common use 

 for recording the strength. This is sometimes given in terms of 

 free SO3, and at other times in termsof HjvSjOy. Table 14 shows 

 the relation between the two methods of nomenclature. 



Table 14. — Concentration of SO^ in fuming sulphuric acid. 



Per cent 



Per cent 



Per cent 



Per cent 



Per cent 



Per cent 



Per cent 



Per cent 



Per cent 



total SO3. 



H2S2O7. 



free SO3. 



total SO3. 



H2S2O7. 



free SOs. 



total SO3. 



H2S2O7. 



free SO3. 



81.8 











85.1 



40 



19 



88.4 



80 



37 



82.6 



10 



5 



85.9 



50 



23 



89.2 



90 



41 



83.4 



20 



10 



86.7 



60 



28 



90.0 



100 



46 



84.2 



.30 



14 



87.5 



70 



32 









The proper proportion in which to mix ordinary concentrated 

 sulphuric acid with fuming sulphuric acid (H2S2O7) is shown by 

 figure 13. 







PCnCEHT or ORDINARY ACID IN m 

 30 « SO 60 



XTUnE 

 70 



e 



J 



90 





















































/ 



A 



/, 



^ 



/ 



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/ 



A 



y// 



// 





* 

















/ 



/ 





//, 



//, 



' 





s 















/ 



/ 



/ 





y^ 



/ 







i. 













/ 



1 



/ 



// 





y^ 



' 













' 









/ 



/ 



/ 







y 



















/ 



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7 







^ 



















/ 



/ 



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0/ 



^/ 



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oAc 



/s/& 





















/'TR 



1 





L 



iL 







:ip 















1 





1 



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t> 







4 











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K 



C'tBCtBT OC 1 



c^CID lU MIXTURE 



Fig. 13.— Proportion of fuming sulphviric acid 

 H2S2O7 required to raise ordinary sulphuric 

 acid to approximately 37. 



Tar acids. — For the most part tar acids were not estimated; when 

 they were, the methods specified by the National Electric Light 

 Association, as giv^en in Part IV, were used. 



