384 NafHraUPhUosophical Collections. 



pounds precipitate solutions of iron of a rusty colour, and the nitrates of silver 

 and protoxide of mercury, in a white flocculent state. The neutral ammoniacal 

 salt crystallizes with difficulty, the acid salt easily. These, when heated, evolve 

 ammonia, and leave principally hippuiic acid. The hippurates of potassa, soda, 

 and magnesia, are very soluble and difficultly crystallizable. The hippurates of 

 baryta and strontia are soluble and crystallizable. The sub-salt of baryta has 

 peculiar properties. The salt of lime crystallizes in rhomboidal prisms, &c., 

 which are anhydrous : they dissolve in 1 8 parts cold water, and 6 parts of boil- 

 ing water ; it consists of 87.28 acid, and 12.72 lime. A neutral, and a sub-salt 

 of lead may be formed ; the former, by mixing a hot solution of a salt of lead 

 with a hippurate, will be obtained, as the mixture cools, in nacreous plates ; 

 these are anhydrous, and consist of 64.38 acid, 35.62 oxide. Other salts have 

 been formed with other bases. 



When the dry hippuric acid is decomposed by heat, there is found, as already 

 stated, a crystalline sublimate, which condenses in tire neck of the retort, and has 

 a yellow or rosy colour ; if much hippuric acid has been used, this substance ul- 

 timately obstructs the neck of the retort. This substance dissolves in hot water 

 easily, and contains ammonia ; when combined with lime, filtered, and separated 

 again by muriatic acid, it has all the properties of benzoic acid ; it forms salts 

 like the benzoates, and, in fact, it is benzoic acid. Hence Fourcroy and Vau- 

 quelin were right when they said they had obtained benzoic acid from the urine 

 of horses ; but it had not existed there ready formed. 



If the hippuric acid be mixed with four times its weight of quick lime and dis- 

 tilled, it is entirely transformed into a yellow oily liquid, with an agreeable odour, 

 containing ammonia, and resembling the fixed oils. If the hippuric acid be 

 mixed with sulphuric acid, and heated only until sulphurous vapours begin to 

 appear, if then the black mass be mixed with water, boiled with lime and then 

 muriatic acid used, benzoic acid may be separated, being formed in this way as 

 well as by heat alone. When the hippuric acid is boiled with nitric acid, a lit- 

 tle nitrous acid is evolved, and then water precipitates pure benzoic acid. 



M. Liebeg remarks, that he has not been able to extract the smallest trace of 

 benzoic acid from the food of horses of which he has examined the urine ; the 

 crystalline form makes him doubt whether the substance which M. Vogel found 

 in the anthoxanthum odoratum, and holcus odoratus, is really benzoic acid, as 

 announced Brande's Journ. June 1830. 



Note on " Active Molecules ,•" by M. Raspail — It was thought that. the 

 subject of the alleged motions of granules had been exhausted, and that people 

 had finally resolved to speak no more about it ; but we do not so cheaply get rid 

 of the learned societies, when some of their members or proteges run astray. Mr. 

 Robert Brown has returned to the charge after a year's silence ; and, in July 

 1829, came to Paris, to distribute, in the Academy of Sciences, a pamphlet of 

 seven pages, entitled Additional Remarks on Active Molecules, printed in Lon- 

 don. 



As, in the number of the Annales des Sciences Naturelles, for October 1828, 

 ]\I. Brongniart took great pains to pass over the objections urged against him, to 

 suppress whatever was most hostile to his opinions, to adduce testimonies whose 

 authenticity we should be induced to deny, as we have testimonies of quite a con- 

 trary nature, and, lastly, to draw up his opinion retrospectively, and shape it, so 

 to speak, upon the model of the refutation ; so, Mr. Brown, after taking due pre- 

 cautions to cover in one way or other the concessions which he makes, in reality 

 overthrows the whole of his first performance, and makes out of it a patchwork ap- 

 parently intended to confirm the first. 



The author had announced, in his first memoir, that all molecules, whether or- 

 ganic or inorganic, are possessed of motion. He had assimilated them to the al- 

 leged spermatic animalcules of vegetables, which M. Brongniart and M. de ^Cas- 

 sini considered as possessed of a spontaneous motion. At present Mr. Brown as 



