Dr. W. Gregory on the Preparation of Hippuric Acid. 129 



As it was clear that the hippuric acid was not in the slight- 

 est degree decomposed by boiling with excess of lime, al- 

 though so easily metamorphosed by acids, I thought that by 

 applying the same principle to the urine directly, I might be 

 enabled to boil it down, and thus shorten the process, and at 

 the same time prevent the decomposition of the hippuric acid, 

 since it would appear that hippurate of lime is not affected 

 by boiling, nor by excess of lime. 



Accordingly, I took some urine of the horse, mixed it with 

 excess of milk of lime and boiled for a few minutes. I then 

 strained the solution, which was very materially decolorized, 

 and boiled the clear liquid as rapidly as possible down to the 

 requisite bulk. On adding hydrochloric acid I obtained a 

 copious deposit of crystals, which when pressed had a slight 

 red colour. I then treated them by Schwarz's method and 

 obtained an abundant crop of almost colourless crystals, 

 which consisted entirely of the needles of hippuric acid, with- 

 out a visible trace of benzoic acid, the crystallization of which 

 is easily recognized. A second treatment with milk of lime, 

 which was hardly needed, and probably would have been 

 quite unnecessary had a greater excess of lime been used in 

 the previous one, yielded snow-white crystals of the utmost 

 beauty and purity. 



The improvement which I have thus introduced in the 

 preparation of hippuric acid may seem trifling, and is indeed 

 only the application of Schwarz's method to the urine, in- 

 stead of to the crude acid ; but any one who tries to prepare 

 some ounces, not to say pounds, of hippuric acid, will soon 

 find that the difference is practically important. By my me- 

 thod it is possible to extract in one day the hippuric acid 

 from as much urine as would require a week to operate upon 

 on the usual plan, so that the quantity of hippuric acid which 

 we can thus obtain is only limited, as it were, by the quan- 

 tity of urine to be procured. The tedious evaporation at low 

 temperatures is got rid of, and we are sure of obtaining the 

 whole hippuric acid originally present ; whereas, on the for- 

 mer plan, however carefully the evaporation is conducted, 

 and it requires constant superintendence, it almost ahvays 

 happens that some of the hippuric acid is decomposed ; while 

 a very slight accidental rise of temperature may destroy the 

 whole of it, as I have often seen. 



On the whole, I am satisfied that all who wish to study 

 hippuric acid and glycocoll will find on trial that what was 

 formerly a disagreeable and troublesome operation is now a 

 very easy and short one ; and that they may now easily ob- 

 tain these remarkable compounds in any desired quantity. 

 Phil. Mas. S, 3. Vol. 3 1 . No. 206. Aus. 1847. K 



