APPENDIX. ANALYTICAL EVIDENCE. 101 



NOTE (42,) p. 156. 



COMPOSITION OF CAFFEINE,, THEINE, GUARANINE, THEOBROMINE, AND ASPARAGINE. 



Caffeine, a Theine. ft Guaranine. c Calculated 

 Pfaff and Liebig.* Jobst. Martius. C8H5N2O2 



Carbon . . 49-77 50-101 49-679 49-798 



Hydrogen . 5-33 5-214 5-139 5-082 

 Nitrogen . . 28-78 29-009 29-180 28-832 



Oxygen . . 16-12 15-676 16-002 16-288 



a Ann. der Pharm., I., 17. 6 Ann. der Pharm., XXV., 63. c Ann. der Pharm., XXVI., 95 



Guaranine is the name given to the crystallized principle of the guarana officinalis, tiLi 

 ft was shown to be identical with caffeine and theine, as the above analyses demonstrate- 



COMPOSITION OF THEOBROMINE. a 



Calculated 

 Woskreseusky. C9H5N302 



Carbon . . . 47-21 46W 4671* 46-43 



Hydrogen .' . 4-53 4-61 4-52 4-20 



Nitrogen . . . 35-38 35-38 35-38 35-85 



Oxyg-en . . 12-88 13-04 13-39 13-51 

 a Ann. der Chem. und Pharm., xli., 125. 



COMPOSITION O* VSPARAGINE.fl 



Liebig. Calculated C8H8N206 + 2HO 



Carbon . . . iJ2-351 32-35 



Hydrogen. . . 0-844 6-60 



Nitrogen , . . 18-734 18-73 



Oxygeu . . . 42-021 42-32 

 a Ann. der Pharm., VII., 146. 



ON THE CONVERSION OF BENZOIC ACID INTO HIPPURIC ACID.* BY WILHELM KELLER 



(From the Annalen der Chemie und Pharmacie.) 



So early as in the edition of Berzelius* "Lehrbuch der Chemie," published in 1831, 

 Professor Wohler had expressed the opinion, that benzoic acid, during digestion, was 

 probably converted into hippuric acid. This opinion was founded on an experiment 

 which he had made on the passage of benzoic acid into the urine. He found in the 

 urine of a dog which had eaten half a drachm of benzoic acid with his food, an acid crys- 

 tallizing in needle-shaped prisms, which had the general properties of benzoic acid, and 

 which he then took for benzoic acid. (Tiedemann's Zeitschrift fur Physiologie, i. 142.) 

 These crystals were obviously hippuric acid, as plainly appears from the statements, that 

 they had the aspect of nitre, and, when sublimed, left a residue of carbon. But at that 

 time hippuric acid was not yet discovered ; and it is well known that, till 1829, when 

 these acids were first distinguished from each other by Liebig, it was uniformly con- 

 founded with benzoic acid. 



The recently published statement of A. Ure, that he actually found hippuric acid in 

 the urine of a patient who had taken benzoic acid, recalled this relation, so remarkable in 

 a physiological point of view, and induced me to undertake the following experiments, 

 which, at the suggestion of Professor Wohler, I made on myself. The supposed conver- 

 sion of benzoic acid into hippuric acid has, by these experiments, been unequivocally 

 established. 



I took, in the evening before bed-time, about thirty-two grains of pure benzoic acid in 

 syrup. During the night I perspired strongly, which was probably an effect of the acid, 

 as in general I am with great difficulty made to transpire profusely. I could perceive no 

 other effect, even when, next day, I took the same dose three times; indeed, even the 

 perspiration did not again occur. 



The urine passed in the morning had an uncommonly strong acid reaction, even aftei 

 it had been evaporated, and had stood for twelve hours. It deposited only the usual sedi- 

 ment of earthy salts. But when it was mixed with muriatic acid, and allowed to stand, 



* To the evidence produced by A. Ure, of the conversion of benzoic acid into hippuric acid in the 

 numan body, M. Keller has added some very decisive proofs, which I append to this work on ac- 

 count of their physiological importance. The experiments of M. Keller were made in the laboratory 

 of Professor Wohler, at Gottingen; and they place beyond all doubt the fact that a non-azotized 

 substance taken in the food can take a share, by means of its elements, in the act of transformation 

 of the animal tissues, and in the formation of a secretion. This fact throws a clear light on the 

 mode of action of the greater number of remedies ; and if the influence of caffeine on the formation 

 of urea or uric acid should admit of being demonstrated in a similar way, we shall then possess the 

 key to the action of quinine and of the other vegetable alkalies. J. L. 



