INDUSTRIAL AND ENGINEERING CHEMISTRY
98
last two residual solutions from these deposits showed no trace of arsenic. This was run as a sample, and a11 the added arsenic appeared in the concentrate.
Literature Cited Anon., Proc. Am. SOC.Testing Materials, 20, I, 589 (1920). Azzarello, E., G a m chim. ital., 39, 11,450 (1910). Breckpot, R., Ann. soc. sci. Brusrlles, 55B, 173 (1935). Britton, H. T. S., and Jackson, P., J . Chem. SOC., 56, 1048 (1934). (5) Brownson, E. E., Bull. Am. Inst. Mining Engrs., 80,1489 (1913). (6) Butler, P., Chem. Engr., 5 , 66 (1907). (7) Classen, A., “Quantitative Analysis by Electrolysis”, p. 233, New York, John Wiley & Sons, 1919.
(1) (2) (3) (4)
VOL. 12, NO. 2
(8) Di Pascal, C., Act. trab. V . congr. nac. mid., 7, 428 (1934). (9) Heath, G. L., “Analysis of (>oPPer”, PI). 196-202, New Yo& McGraw-Hill Book Co., 1916. (10) Heath, G. L., J. IND. EXQ.CHEM.,3, 78 (1911). (11) Hollard, A., and Berteaux, L., Bull. SOC. chin., 23, 300 (1900). (12) Keffer, R., “Methods in Non-Ferrous ?vIetallurgical Analysis”, p. 114, New York, McGraw-Hill Book Go., 1928. (13) Kein, E . F., and Ching Yu Wen, M e t . Chem. Eng., 9, 365 (1911). (14) Leighton, A. E., Australia Dept. of Defence Munitions Supply Board, May, 1926. (15) Nitchie, C. C., IND.EKQ.CHEM., Anal. Ed., 1, 1 (1929). (16) Scott, W. W., “Standard Methods of Chemical Analysis”, 2nd ed., p. 33, New York, D. Van Nostrand Co., 1920. (17) Torrance, S.,Analyst, 63, 104 (1928).
Qualitative Test for Ethyl Vanillin in Vanilla Extract HOWARD W. CHENOWETH Virginia Dare Extract Co., Inc., Brooklyn,
The undeclared addition of small amounts of ethyl vanillin to pure vanilla extracts constitutes an adulteration which cannot be detected by the usual methods of analysis. A new method definitely indicates the addition of 0.5 gram or more of ethyl vanillin to 3.785 liters of vanilla extract. The source or kind of vanilla bean used does not affect the results. The test is simple to perform and onlv usual laboratory reagents are required.
T
HE ethyl ester of protocatechuic aldehyde is known
erroneously as “ethyl vanillin” and commercially bears several trade names, the most popular of which is “Bourbonal”. I n intensity of taste and odor, this compound is three to four times as strong as vanillin. Ethyl vanillin melts approximately 4” C. lower t h a n regular vanillin but the compounds are chemically similar. Since ethyl vanillin possesses such flavoring strength and reacts in so many ways like vanillin, the flavor manufacturer is tempted to fortify his pure vanillas by the judicious additions of small amounts of ethyl vanillin. Such small additions, usually on the order of a few grams per gallon, materially strengthen the flavor of the product b u t do not alter the analyses sufficiently t o indicate adulteration. The determination of the melting point of the residue from the ether extraction does not indicate the presence of ethyl vanillin unless a considerable quantity has been added. A search of the literature shows no chemical tests t h a t indicate the addition of ethyl vanillin to vanilla extract. However, several reports (2, 3) published in Germany set forth methods for chemically distinguishing vanillin and ethyl vanillin in the pure state and in mixtures with powdered sugar. T h e writer has devised a modification of these methods, by which t h e addition of as little as 0.5 gram of ethyl vanillin to 3.785 liters (1 gallon) of vanilla extract is easily and definitely detected. Several samples of commercial vanilla extracts which purported to be pure were examined and gave
N. Y .
very positive results, indicating the addition of ethyl vanillin and proving the exist’ence of this type of adulteration.
Procedure Dealcoholize 50 cc. of the sample, treat with lead acetate solution, and extract with ether in exactly the manner prescribed in the official A. 0. A. C. gravimetric method for vanillin ( 1 ) . Place the ether extract in a sma.11 beaker and allow the residue to remain overnight in a desiccator. Then add 1 cc. of an acid solution made by diluting 2 parts of concentrated hydrochloric acid with 1 part of water. Place the beaker in a water bath at 55” C. until the residue is dissolved, then pour the solution into a medium-sized test tube. Use no wash water, as a quantitative transfer is not required. Add 1 cc. of 3 per cent hydrogen peroxide solution to the test tube, and shake frequently while the color changes to yellow, brown, then red. Finally a deep purple color appears and a blue precipitate forms. After standing 15 minutes add 5 cc. of benzene and place the test tube in the water bath at 55’ C. Shake frequently and allow the test tube to remain in the water bath until the lower aqueous layer becomes a dirty yellonish brown (about 15 to 20 minutes). Then remove it from the water bath and carefully pour or pipet a major portion of the benzene layer into a small dry test tube. If the benzene is colored violet,, ethyl vanillin is present in the original sample. In the absence of ethyl vanillin, the benzene is colored a light or dirty yellov.
Discussion Several different compounds ‘have been identified in vanilla extracts prepared from beans of varying geographic originfor example, cinnamic acid esters from Bourbon beans, and anisic alcohol and aldehyde from Tahiti beans. For this reason, standard extracts were prepared from Mexican, Bourbon, Tahiti, and Java beans and blank determinations were carried out on these samples. I n no case was the slightest positive result obtained, indicat’ing that the origin or variety of the bean does not affect the results of this test. I n a n endeavor to establish t’he fact tihat this method is specific for ethyl vanillin, tests were carried out with the addition of coumarin, heliotropine, and several so-called “vanillin esters”. None of the compounds tested gave the characteristic violet color which the presence of ethyl vanillin imparts to the benzene layer, and, therefore, i t is safe to assume that of the various compounds which might logically be encountered, this method is specific for ethyl vanillin. A series of experiments was made to determine the sensitivity of this method, and it mas found t h a t the addition of 13.2 mg. of ethyl vanillin to 100 cc. of standard vanilla extract
Estimation of Small Amounts of Arsenic in Copper B-IKTHOLOW P.LRh JIichigan College of >lining and Tcchnolop? , Houghton. \Iiah.
THREE
hydroxide, and i~ known amount, 20 mg., of pentavalent arsenic was added to each. Electrolysis was carried out with a current of about 2 amperes at about 2 volts until all but a small amount of copper had been deposited. The deposited copper \vas redissolved and electrolyzed again under the conditions described for the preparation of arsenic-free copper. Each solution contained 10 grams of copper in a volume of 350 cc.
ways of separating arsenic from copper are i n general use, each depending upon a different property. The insolubility of copper arsenate in slightly acid (6, 10, 14) or ammoniacal ( 3 , 6 , 9, 12) solution is the basis of tlie precipitation met'hod. All the arsenic niay be removed from copper in this way hut' the procedure is slow, requiring the filtration of large amounts of liquid containing ferric hydroxide, which is added as a collector. The volatility of arsenious clilo1,ide rnakcs possihle its separation from copper by distillation (1, 2 , 9, 11, I S , 16). This method gives fairly good result5 \Then rather large amounts of arsenic are involved but is open to criticism on several scores: Coinparatively large anmints of cuprous chloride or ferric chloride are usually added, eitliei, of n-hicli may contain more arsenic than the copper to lie analyzed, special apparatus is required, and the last traces of arsenic are hard t o expel. Tlic third wq'of separating the two nietals tlepentls u p i n tlieir different behavior n-lien a current is pas.setl tlirough a strongly acid solution containing tlieni. The electrolytic: separation of copper f r o m arsenic ('7, 9) has Iieen kiio\vn for a long time, and may be carried out simply antl accurately) although Heath states ( 9 ) that electi,olytic separations cannot be considered as relia1)le as iiietliods in n-liich the arbenic group is separat,ed from the h l k of the coppei, 1)y a special precipitant .
TABLEI. DsPosI,rIox OF ARSEXIC HSOa
hrseiiic Depositeil
cc.
.My. '0
I
1j
ace Sone Sone Sone Ti
The rcaidts (Table I) show that pentavalent arseiiic does not clepobit ivitli copper if sufficient nitric acid is present. Torrance ( I ? ) lias s h o ~ v nthat triralent arsenic will deposit from hydrocliloric acitl solution hut' that tlie pentavalent form will not. It \vab tliouglit atiyisahle t o check this work and also to fiiitl out n-liether trivalent arsenic \voultl tlepobit from a nitric aci(l solutioii. A icrie-: of runs ivas made, the r,esults of wliicli are gi\-en in l'alile 11. In c a d i case 10 grains of copper tlimJvetl in 20 cc. uf conc.etiti~atetle u l f w i c acid antl 20 cc. of concentrated nitric acid were present i n a volume of aliout 350 cc. Because t~,ivalent arbenic forms a complex witli tartaric acitl ( 4 ) , m i l e tartaric acid was acldetl to fiiicl out \vliether or not it.; Ixe-ence I\-ould retard the dcpositioii of arsenic. Runs were alw made to see ivhetlier larger anlourits of arsenic could lie succewfully separated.
Preparation of hrsenic-Free Copper Arsenic-free copper was prepared from refined copper loiv in arsenic by electrolyzing 10 grams of copper dipsolved in 20 re. of concentrated sulfuric acid and 20 cc. of concentrated nitric acid in about 100 cc. of wat,er. Aft,er the brown fumes were boiled off about 10 grams of tartaric acid were added and the solution v a s diluted to about 350 cc. A large platinum gauze cathode and a platinum wire anode v-ere used. A current of about 4 amperes at about 2.5 volts was allowed to flow until nearly all the copper had been deposited and the solution was faintly blue (about -1 hours). The deposited copper v a s removed from the solution, washed \\-ell, and then dissolved and reelectrolyzed as before. The copper \vas dissolved a third time, 0.5 mg. of arsenic added, and the electrolysis repeated. Each of the three residual solutions was neutralized with amnionium hydroxide and then acidified with 3.4 cc. of 1 to 1 hydrochloric acid per 100 cc. as recommended by Di Pascal (8). Hydrogen sulfide \vas passed through the hot solutions until they cooled. The sulfides vere filtered off on a Jena glass filter and boiled wit,h concentrated nitric acid. The solutions of the sulfides were filtered and then concentrated to 5 cc., 0.4 cc. of the concentrates was measured into holloved graphite electrodes, and the dried electrodes were subjected to $pectiographic analysis.
TABLE11. DEPOSITIOX OF T R I K ~ L E S ;IKSENIC T HC'I I'C.
I (I 10 10
Arsenic Depileire
