urbaf2

NITRATION WITH NITRATING MIXTURES 145

be carried out at higher temperatures without any risk of exceeding the safety limit

and due to the higher temperature, nitration can proceed more rapidly.
Gelfman [5] has revised the generally accepted data for calculation of the heat

generated during mixing the acids and during their dilution with water [16]. He found

the absolute value of the heat generated in the reaction between sulphuric and

nitric acids to be lower in the presence of water than when the acids are in an an-

hydrous state. He also found it decreased on diluting the acids with water. This

relationship presented graphically is close to a linear one (Fig. 19). On the diagram

TABLE 17

PHYSICAL PROPERTIES OF SULPHURIC ACID

Specific gravity H 2 SO 4 %

Specific heat

cal/g

1.84 98.5 0.33

1.82 90.0 0.36

1.77 83.4 0.38

1.71 77.5 0.41

1.61 69.0 0.45

1.53 62.5 0.49

1.45 55.0 0.55

FIG. 19. Heat evolved on mixing nitric acid with sulphuric acid

in relation to the water content A in these acids. Quantity of heat

Q = A B (Gelfman [5]).

A is the percentage of water in the mixture and B the coefficient of the thermal

effect of mixing the acid, It ranges from 1 (maximum value) for anhydrous acids,

and is zero for water. The thermal effect of mixing hydrated acids will be expressed

by the product B*Q, where Q is a value taken from another of Gelfman’s

diagrams (Fig. 20).