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NITRATION WITH NITRATING MIXTURES 141

= 2.96, is incomplete, while with the B mixture, where D.V.S. = 3.5, results in

complete nitration. The mixtures have the following composition:

A HNO 3 38.0%, H 2 SO 4 54.0%, H 2 O 8.0%

B HNO 3 32.0%, H 2 SO 4 60.0%, H 2 O 8.0%

The nitrating acid and its weight should also be carefully chosen so as to obtain

a spent acid with a composition corresponding, where possible, to the lowest solu-

bility of the nitration product in it.

In the U.S.S.R., the D.V.S. is often named the coefficient of dehydration and
a slightly different way of calculating the nitric composition of sulphuric acid
mixtures is in use there. This is Φ or “f.n.a.“, the factor of nitrating activity sug-

gested by Kholevo. According to Gorst [2], it is the concentration of sulphuric

acid in the mixture when the nitric acid is converted into the equivalent quantity

of water.

Here is the method of calculating Φ according to the same author.

Let the symbols S, N, S’ denote the following:

S - % concentration of H 2 SO 4 in the mixture

N - % concentration of HNO 3 in the mixture used for nitration

S’ - % concentration of H 2 SO 4 in the spent acid, when all the nitric acid N is used

and from 1 mol. of HNO 3 1 mol. of H 2 O is formed.

One kg of HNO 3 yields z = 0.286 kg of H 2 O.

The weight of the nitrating mixture is therefore reduced by l-0.286 = 0.714 kg for every kg

of HNO 3. The reduction of the weight of 100 kg is 0.714 N.

The concentration of H 2 SO 4 in the spent acid S’ will be:

S’ = l00 S

100-0.714 N

or

140 S

S’ =

140-N

The expression for is:

or

It is not advisable to use a high value of the factor of nitrating activity Φ for

economic reasons. Nor should low Φ, be applied as this leads to incomplete utiliza-

tion of the nitric acid in the nitrating mixture.

Orlova [3] gives a number of examples of the values of Φ and of the quantity

of HNO 3 used during the nitration (Table 15).