Five c.c. of the wood naphtha are run into a silver pressure flask of about 150 c.c. capacity, together with 20 c.c. of recently boiled distilled water and 10 c.c. of normal soda solution; the flask is then securely closed and digested for at least two hours in a water-bath at 100°. The contents are then cooled, washed into a beaker, and titrated with iV/1-acid and phenol-phthalein. Deduct the number of c.c. of acid required from 10; the difference X 1.48 = grams of esters, calculated as methyl acetate, per 100 c.c. of the naphtha.

Fig. 37. - silver pressure flask.

Used for determining esters in wood-naphtha.

1 Ber., 1888, 21, 336G.

Or more generally: - Grams methyl acetate per 100 c.c. = c.c. of soda solution used up in the hydrolysis X 0.074 X

100 / c.c. naphtha taken.

If the naphtha is not neutral to phenolphthalein, it must be neutralised before the esters are determined. Instead of using a silver pressure flask, the hydrolysis may be carried out in a hard glass flask fitted with a reflux condenser, and heated on a water-bath.