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 with enough 
ordinary sulphuric acid so that the finished mixture will contain 
80.1 per cent S0 3 . 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 S0 3 , and at other times in termsof H 2 S 2 7 . Table 14 shows 
the relation between the two methods of nomenclature. 
Table 14.— Concentration of S0 Z 
in fuming sulphuric acid. 
Per cent 
total S0 3 . 
Per cent 
H2S2O7. 
Per cent 
free SO3. 
Per cent 
total SO3. 
Per cent 
H2S2O7. 
Per cent 
free SO a . 
Per cent 
total S0 3 . 
Per cent 
H2S2O7. 
Per cent 
free S0 3 . 
81.8 
82.6 
83.4 
84.2 

10 
20 
30 

5 
10 
14 
85.1 
85.9 
86.7 
87.5 
40 
50 
60 
70 
19 
23 
28 
32 
88.4 
89.2 
90.0 
80 
90 
100 
37 
41 
46 
The proper proportion in which to mix ordinary concentrated 
sulphuric acid with fuming sulphuric acid (H 2 S 2 7 ) is shown by 
figure 13. 
30 
PEOCEMT or ORDINARY 6CI0 
40 SO 6 
in m 

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70 
80 
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{•ESCtSTT C7 ruKlliC i«ID It) MIXTURE 
Fig. 13.— Proportion of f ilmi ng sulphuric 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 given in Part IV, were used. 
