Directions for Laboratory Work in Physiological Chemistry.
Journal: JAMA (1904)

THE CARBOHYDRATES.The term carbohydrate is usually considered as embrac- ing those compounds which contain the elements C, H, and 0, the H and being present in the same ratio as they exist in water.This definition, strictly followed, would include in the group substances such as lactic acid, acetic acid, and inosit, which are obviously not carbohydrates.The carbohydrates may be conveniently divided into three groups; namely, Monosaccharides or Glucoses, Disaccharides or Saccharoses, and Polysaccharides or Amyloses ; but a more strictly chem- ical classification would designate them according to the number of carbon atoms present in the molecule, the prefix aldo-or keto-denoting to what general class of compounds (aldehydes or ketones) they belong: thus trioses, tetroses, pentoses, hexoses, heptoses, etc., and aldohexose, ketopen- tose, etc.Of the greatest physiological importance are the pentoses, hexoses, hexobioses (Disaccharides), and polyoses (Amyloses).Note the general character and appearance of the vari- 2 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY ous specimens of carbohydrates which are presented for study.Test for the constituent elements as follows:(a) Carbon.1.Heat cautiously some of the substance on a platinum foil.The piece will char, owing to the sepa- ration of the carbon in the substance.Further heating ren- ders the carbon capable of combining with the oxygen of the air, with the result that the former passes off as C0 2 , and in the case of carbohydrates, where combustion is complete, no residue is obtained.A substance containing oxy- gen in sufficient quantities to form C0 2 with all the carbon present will not carbonize.2. Mix thoroughly some of the dried substance with powdered CuO and place the mixture in the bottom of a dry test-tube.Upon warming, the carbon of the substance is oxidized by the oxygen of the CuO and escapes as C0 2 .This C0 2 may be detected by holding a glass rod moistened with lead acetate at the mouth of the test-tube.(b) Hydrogen. 1.In the latter experiment, moisture will have collected on the cold part of the test-tube.The hydro- gen of the substance, in the presence of heat, has combined with the oxygen supplied by the CuO, forming H 2 0. PENTOSES, C 5 H 10 5 . ARABINOSE XYLOSE.The pentoses do not occur free in nature, but exist in the form of pentosanes bodies which are found in the fruits and polysaccharide gums (e.g., gum arabic, cherry gum) and from which the pentoses may be obtained by hydrolysis with weak acids.The ingestion of pentosanes also causes pento- ses to appear in the urine.Chemically they are aldehydes and as such reduce Fehling's solution.With regard to their THE FATS.13 Emulsification of Fats.Certain poorly understood factors enter into the formation and preservation of an emulsion.Apparently the viscosity of the menstruum and the condition of the surface tension existing between that menstruum and the globules form the fundamental physical requisites for the obtaining of a permanent emulsion.Solutions of gums, proteids, and soaps emulsify fats with varying degrees of permanency.The mere presence of a soap in the solution does not seem to render the fat particularly prone to emulsify; the necessary condition is apparently the intermodular forma- tion of a soap in the solution as exemplified upon the addi- tion of an alkali to fat containing some free fatty acid.An emulsion formed in this manner is the most permanent of all those induced by artificial means; a similar procedure takes place in the emulsification of fat in the intestine.Make up the following mixtures in test-tubes :(a) 2 drops of neutral olive oil + 10 c.c. water.(&) 2 drops of neutral olive oil + 10 c.c. water + a few drops of Na 2 C0 3 .(c) 2 drops of neutral olive oil + 10 c.c. of the soap solu- tion.(d) 2 drops of neutral olive oil + 10 c.c. of an egg-albumin solution.(e) 2 drops of rancid olive oil + 10 c.c. of water + a few drops of Na 2 C0 3 .Shake each tube approximately the same length of time and compare the relative permanence of the various emul- sions.Which conditions are the most favorable, and why? 14 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY.CH 2 OH I GLYCEROL, CHOH CH 2 OH.Make use of the solution obtained from the two saponifica- tions for the following tests:(a) Note the taste and try its solubility in alcohol; ether;water.(6) Add some dry potassium bisulphate and warm.Compare this with the same reaction under Fats.Write the equation.(c) Test with Fehling's solution.(d) Precipitate a small amount of Cu(OH) 2 , and to this add the remainder of the glycerol solution.What happens?.