620 CRIC.WID METABOLISM AXD GOUT 



Properties of Uric Acid. — Uric acid, when pure, is white, and 

 crystallizes in rhombic tablets. Its solubility is very slifi'ht ; at room 

 temperature (18°) it dissolves but about one part to 40,000 of water, 

 so that a saturated solution contains but 0.0253 gram to the liter. 

 It is much more soluble in blood-serum, dissolving in 1000 parts,^ 

 ])robably held in some complex combination. His and Paul have 

 shown that in a saturated solution oidy 9.5 per cent, of the molecules 

 are dissociated, tlie dissociation occurring in two steps; the Urst and 

 chief dissociation is into H and C.,H..5N^0.j, which then undergoes fur- 

 ther dissociation into H and Cr.HoN^O.,, the latter dissociation being 

 very slight. If any other acid is present in the solution, its dissocia- 

 tion and liberation of free hydrogen ions interferes with the dissocia- 

 tion of the uric acid, and as the undissociated uric acid is extremely in- 

 soluble, the amount dissolved in an acid solution is much less than in 

 a neutral solution.^'' Gudzent * found that saturated solutions of 

 urates gradually precipitate out the salts because of a transformation 

 of part of the uric acid into what he believes to be a I-actim form. 

 (The lactim form is shown in the following formula, as compared with 

 the isomeric lactam form shown above, in which uric acid is supposed 

 to exist ordinarily.) 



N = C — OH 



With alkalies uric acid yields two series of salts, corresponding 

 to these two steps in dissociation : one, in which one atom of the base 

 enters, is called the hiurate or monohasic urate ; the other is the so- 

 called ''neutral" or hihasic urate.''' Of the two, the latter is much 

 the more soluble. The monosodium urate forms colloidal solutions 

 in water, from which the crystalline salt gradually falls out. The 

 quadriurate, of which much was said in the earlier literature, prob- 

 ably does not exist (Kohler).*' 



In the urine the uric acid and the urates are kept in solution by 

 the pliosphates, the disodiuui phosphate preventing the decomposition 

 of tlie urates into uric acid by the acid salts of the urine. Possibly 

 other constituents of the urine, especially the pigments and NaCl, also 

 aid in its solution. Urine may form quite stabl(» supersaturated solu- 

 tions and Kohler states that the urine is a ti'uly suix'rsaturated solu- 



s Taylor, Jour. Biol. Cheni., IDOG (1), 177. 



3a Concorniiitr tlio sohibilitv of uric acid in urine sec I[a>kiiis, .lour, liiol. Clieiii., 

 I'tlO (26), 205. 



«Z('it. pliysiol. Chcin., I'KI!) ((iO), .38. 



•'■' .Xs <'i. matter of fact, l)olli salts ^ive a sli<ililly alkaline reaction wlien dis- 

 Holved in water ('i'a\lor). 



'■Zeit. physiol. Cliom., 1!)11 (72), 10!); 1!)13 (78), 205. 



