Monthly record of analytical researches into food

1885 The Analyst  
Centralblatt f u r die Medicinischen Wisscnschaften, 1882 , p. 209.-If a solution containing albumen be acidulated with formic acid, and a solution of gold chloride (0.1 per cent.) be added, drop by drop, the mixture being warmed, Bubbles of gas are formed on the sides of the test-tube; the solution turns first roso-red, and then assumes a beautiful purple-red ; on further addition, a blue colour ; finally, a blue flocculent precipitate separates out. The rate of change to blue is in proportion
more » ... to the dilution of the solution of albumen. The blue or violet coloration is also caused by other organic substances, such as grape-sugar, starch, glycerine, leucine, tyrosine, creatine, uric acid, and urea. Pure gelatine gives a dichroic brown or reddish coloration. Impure gelatine (probably containing albumen) gives, when sufficiently concontrat ed, the purple colour. Gum solutions give also a beautiful purple-red uolouration, which diff em, however, from the albumen reaction by changing to orange-yellow on the addition of potash or soda. The reaction can be made to succeed with pure albumen solution of a dilution of 1 in 1,000,000. The presence of salt, urea, uric acid, or grapc-sugar does not interfere, when not present in excess; otherwise it is only necessary to use more formic acid and gold chloride. F. H. E. TIIE DETERMINATION OF CASEINE IN Cow's MILE.-BY (3. FRENZEL and T. WEYL.1-Zcsitsch. f im Physiologish. Chemic., 9, 246.-The authors conduct the determination for technical purposes in the following way :-30c.c. of tho wcll-sl-taken milk are measured out with a pipette, and mixed with G0c.c. water; the mixture being Tell stirred, 3Oc.c. of a 1 per cent. solution of sulphuric acid are added. TIE cascino lwecipitate is brought (after having been allowed to stand for scveral hours in the cold) on to the filter with water, washed with alcohol and ether, dried, weighed, and ignited. Zeitsch. fur Anal. Chem. 24, 3, 463. About one grm. of the flour to be examined is well rubbed up with 50 C.C. water, and the mixture gradnally warmod on the water-bath to exactly 62-5"C ; on reaching Ihis temperature, the beaker is removed from the bath, cooled with cold water, and the starch grains examined with the microscope. The rye-starch grains become, at 62.5'0, nearly all swollen up ; the most burst, and almost all have lost their original form. The wheat-starch grains, on the other hand, remain mostly quite unaltered, as strongly refractive as normal starch grains, and show, consequently, sharp black borders, while the rye-starch grains, even when they keep their shape, show soft outlines. For the sake of comparison, it is best to make parallel experiments with pure wheat and rye. By the means of this test, we should be able to detect an addition of 5 per cent. wheat to rye, F. H. H. -* Anleitug m Erkennung organischer und ariorgamischer Beimongungen im Roggen und Weizenmehl. t. Pharm. Zeit. 29, 831, $ Pharm. Zeit. 58, 829.
doi:10.1039/an8851000167 fatcat:rfwexpt3rzcdpji5xvkdmbk6qq