842
T H E ] O U R N A L OF I N D U S T R I A L A N D ENGINEERIiVG C H E r l f J S T R Y .
tein than cold alcohol, there does not appear t o be any advantage in its use. 3 . Alcohol varying in strength from 4 j per cent. t o 5 5 per cent. b y weight extracts more protein than alcohol of any other strength, hence it is recommended t h a t j o per cent. b y weight alcohol be used for the determination of gliadin in wheat flour, and that the use of 7 0 per cent. alcohol, whether b y weight or b y volume, be discontinued. DIVISIONO F AGRICULTURAL CHEMISTRY A N D S O I L S , MINNESOTA EXPERIMENT STATION, ST. P A U L .
THE DETECTION OF BENZOIC ACID IN COFFEE EXTRACT. By HERMANc I.YTHGOE A N D CL.4RENCE E Recerved July 21, 1911
MARSH
I n testing a sample of coffee extract for benzoic acid by extracting with ether and testing the ether extract in the usual way with ferric chloride, a precipitate was obtained corresponding to ferric benzoate except in color, but on subliming this precipitate the crystals did not have the characteristic appearance of benzoic acid. A portion of the original sample was then acidified with phosphoric acid and subjected t o distillation with steam. The distillate was made alkaline with sodium carbonate, evaporated t o about 5 0 cc., acidified, extracted with ether, and the ether extract was extracted with ammonia. The ammoniacal solution was then evaporated until free from ammonia and ferric chloride was added which produced a precipitate with the same characteristics as in the previous instance. A sample of coffee extract was then made from pure coffee, and upon repeating these tests this extract was found t o act the same as the commercial extract. A large number of coffee extracts were made from different varieties of coffee and in all cases they reacted in the same manner. The ammonium salt of this substance which was extracted with ether was found t o give precipitates with salts of manganese, nickel, magnesium, calcium, and barium, as well as salts of iron and copper, while benzoates will produce precipitates only with salts of iron and copper, and from these differences the following
Nov.,
1911
method for the detection of benzoic acid in coffee extract has been devised: Make the solution acid and extract several times with ether. Wash the combined ether extracts with water and extract with ammonia. Evaporate the ammoniacal extract to a small volume, adding ammonia from time to time t o prevent it from becoming acid, and add a solution of manganese sulphate. Filter through a small filter, wash with as little water as possible and add ferric chloride t o the.filtrate when a dark greenish precipitate will occur if benzoic acid is present. Evaporate to dryness in the casserole in which the precipitation was made, and sublime b y placing an inverted funnel covered with a filter paper in the dish and heating over an asbestos gauze. Remove the funnel, and determine the melting point of some of the crystals which, if benzoic acid, should be 12I .4 ' C. The rest of the crystals may be dissolved in ammonia, the excess of ammonia evaporated a n d ferric chloride added, when the characteristic fleshcolored precipitate will occur if benzoic acid is present. For quantitative purposes the method of Edmund Clark1 was employed with good results as the natural reacting substance has but little influence. Determinations made on pure extracts b y this method gave from 0.01 t o 0.04 per cent. benzoic acid and a correction can be readily made if desired. The accompanying table gives the analyses of a sample of coffee extract made in the laboratory and of two commercial extracts, one of which contained benzoic acid and glycerine, being very deficient in coffee: ANALYSESOF COFFEE EXTRACTS.
Made in laboratory.. Commercial. .. . . . . Commercial.. . ... . .
.
1.059 1,057 1,070
13.56 13.40 21.42
2.50 2.29 0 93
0.22 0.17 0.58
0.36 0.42 0.15
0.67 0.70 0 14
. .. . .. . . 0.19
DEPARTMENT OF FOOD AND DRUGINSPECTION. IvASSACHUSETTS S T A T E BOARDOF HEALTH, BOSTON.
PLANTS AND MACHINERY ment of different gases demonstrating the practicability of the method for commercial purposes. The reasoning on which the operation of the meter Received September 5 , 1911. is based is this: The specific heat of most gases is The application of the electric meter t o commercial measurement of gases first suggested itself t o Pro- a quantity already accurately determined and i t is fessor Carl C. Thomas while carrying on extensive known t h a t this value changes but slightly through experiments on the specific heat of superheated steam wide ranges of temperature and pressure. If a n at Sibley College and the University of Wisconsin. electric heater be placed in a pipe line through which These investigations required the use of some form there is a constant flow of gas, and the heater give of heating device. The difficulty of direct quantitive off heat a t a constant rate, the gas temperature is measurements of heat except b y electrical measuring raised a certain fixed amount. Any change' in gas instruments finally required the adoption of electric flow under these conditions will mean a change in heaters. The great convenience of these heaters its temperature increase, an increase in gas flow in this work led t o a series of tests on the measure*Science, Aug 20, 1909 p 253 THE THOMAS GAS METER. B y H . N. PACKARD.
