93 



CHEMISTRY. 



solution of iodine corresponding to 0.1 gramme 

 of tannin must be deducted the volume of the 

 solution required to produce the colored reac- 

 tion upon starched paper. For this purpose 

 10 c.c. of distilled water are measured out, 

 mixed with 2 c.c. of alkaline solution, and the 

 solution of iodine is then added, drop by drop, 

 till a spot is obtained upon the starched paper. 

 With a solution containing 4 grammes iodine 

 per litre the correction is generally 0.1 c.c. for a 

 volume of 10 to 12 c.c., but the greater or less 

 purity of the carbonate of soda may make a 

 slight variation in this correction. To 0.01 

 gramme of tannin dissolved in 10 c.c. of water 

 it is generally necessary to take 10.5 c.c. of a 

 solution at 4 per 1,000. The paper used is 

 white filter-paper, covered by friction with a 

 slight layer of powdered starch. For ordinary 

 determinations tannic acid may be taken as 

 the type of the active principle of astringent 

 bodies. Bat, if a high degree of accuracy is 

 required, the solution should be standardized 

 with a pure sample of the astringent body 

 under examination, catechuic acid being used 

 in case of catechu, morintannic acid for fustic, 

 etc. Crystalline gallic acid decomposes the 

 solution of iodine in the same proportion as 

 tannic acid. If it is desired to determine these 

 acids separately, we first find the joint amount 

 of tannic and gallic acids, and then, operating 

 on a fresh portion, remove the tannic acid by 

 means of raspad hide or gelatine and alcohol, 

 and determine afresh the gallic acid remaining. 

 The tannic aoid is then found by subtracting 

 the second result from the first. The extractive 

 matters found in astringents do not interfere. 



Coffee Adulteration. Prof. G. C. Wittstein, 

 in an article contributed to Dingler* Poly- 

 teclmisches Journal, and translated by C:irl 

 Bauer for the American Chemist, discusses the 

 subject of detecting adulterations in coffee. 

 According to the author, masses of dough, 

 moulded after the true bean, are sometimes 

 sold for coffee. Unlike the genuine, these 

 fictitious beans always have sharp edges, and 

 may be very easily ground to a grayish-yellow 

 powder. Boiling in water reduces them to a 

 pasty mass, which, on addition of iodine, as- 

 sumes a deep-blue color. The poorer classes 

 of genuine coffee-beans are variously treated, 

 so as more or less to resemble the better grades. 

 Thus, the coffee is placed, with a quantity of 

 shot, in a barrel, which is rolled about until 

 enough lead has been rubbed on the beans to 

 give them a glossy appearance. This adulter- 

 ation can be detected by the use of a lens ; but, 

 when absolute certainty is desired, the beans 

 should be digested in dilute nitric acid ; then 

 the liquid should be decanted after one hour, 

 diluted with three times its volume of water, 

 and the lead precipitated with sulphureted 

 hydrogen. 



Another substance for coloring coffee is a greenish 

 powder, 100 parts of which are composed of 15 parts 

 Prussian blue, 35 parts chroraate of lead, 35 parts of 

 a mixture of clay and gypsum, 15 parts water. 



The microscope alone is frequently sufficient to 

 discover this adulteration. For more accurate ex- 

 amination, however, it is better to put a considera- 

 ble quantity of the beans in a suitable vessel, and to 

 pour distilled water upon them. After two hours 

 or so, the beans are removed and the turbid liquid 

 allowed to settle. In presence of gypsum the super- 

 natant clear liquor will become densely turbid on 

 addition of baric chloride and ammonic oxalate. 

 Prussian blue may be detected in the sediment by 

 giving rise to a brown coloration on addition of 

 KHO. If this change of color should not occur, the 

 mixture will not contain Prussian blue, but probably 

 indigo. The color of the latter may be destroyed by 

 nitric acid. The potassic hydrate will likewise de- 

 compose the plumbic chromate, to a greater or less 

 extent, causing it to dissolve partially or wholly in 

 the alkali. Turmeric, if present, would merely turn 

 dark brown. If, upon slightly moistening the sedi- 

 ment with sulphide of ammonium, a black color is 

 produced, no further doubt need be entertained as 

 to the presence of chrome-yellow in the mixture. 



By the process of roasting, coffee is put into a 

 condition which renders adulteration almost impos- 

 sible, so long as the beans remain unground. Ground 

 coffee is one of the easiest substances to adulterate. 

 The most usual adulterants are chiccory, beans, peas, 

 as also beets, carrots, and other roots resembling the 

 turnip in properties. 



As all these preparations undergo the same treat- 

 ment as pure coffee, namely, of roasting to a deep- 

 brown color, in many particulars they resemble the 

 genuine article very closely. They cannot, however, 

 be used as a true substitute for the latter, as all are 

 without the most important constituent of pure coffee, 

 namely, caffein. 



The following is a very convenient test: The 

 suspected coffee is poured out on water. If pure, 

 the particles will float and remain in a state of sus- 

 pension for hours ; whereas chiccory will sink im- 

 mediately. A better method is as follows : If to 30 

 drops of the coffee decoctionj in a test-tube, 2 drops 

 of concentrated hydrochloric acid be added, and 

 then, after a few seconds' boiling, the liquid be 

 treated with 15 drops of a solution of 1 part red prus- 

 siate of potash, and 8 parts of water, and again 

 boiled as before, the liquid will first turn green, 

 finally blackish green. Upon now adding to the 

 mixture 6 drops KHO, the liquid, after 4 minute's 

 further ebullition, will become brown, and shortly 

 after, with the deposition of a dirty-yellow precipi- 

 tate, clear, pale yellow. If the chiccory decoction is 

 subjected to the same treatment, the last liquid will 

 be brown and turbid, and only after long standing 

 will a precipitate be deposited while the supernatant 

 fluid retains its brown color. By testing in the same 

 manner a mixture of 6 drops of chiccory and 24 of 

 coffee, the brown turbidness will also be obtained. 

 It is thus easily possible to discover adulterations 

 of chiccory in coffee. 



The quantity of coffee actually dissolved in a de- 

 coction is perhaps always overrated. A good, by no 

 means weak, infusion, left upon evaporation a resi- 

 due of 1 per cent., and a very strong infusion scarcely 

 2 per cent. This residue has the appearance of a 

 dark-brown shining varnish, which is scarcely hy 

 groscopic. at least remains dry after two days' ex- 

 posure. If, however, the coffee contains one of the 

 artificial preparations above referred to, the residue 

 will become sticky to the fingers within 2 hours, and 

 will, after 24 hours, be decidedly moist. This sim 

 pie process may likewise be used as a test upon sus- 

 pected coffee. 'Even the impurity in coffee, chiccory, 

 is subject to various adulterations ; among others 

 with bog-turf. According to Prof. Th. Schwartz, of 

 Ghent, this fraud is practised to a considerable ex- 

 tent, especially in Flanders. 



Antiseptic Properties of Boracic Acid. 

 Prof. Mauricio Schiff, of Florence, after ex- 



