238 Mr. Venables on Siliceous Gravel. 



children. She first consulted me on the 22d of October, 

 1829, complaining of very severe and excruciating pains in 

 the back and loins. The pain also passes along the course of 

 the ureter from the kidney to the bladder. She now, for the 

 first time, perceived a reddish-looking sand at the bottom of 

 the vessel (a tea-cup), in which the water was made. The 

 urine was extremely scanty, not making # much above half a 

 tea-cup full at several times. She brought the specimen with 

 her, and on looking at the bottom of the cup, I saw a very 

 small quantity (about *8 of a grain) of a reddish-looking 

 sand, which I took for lithic acid, the minute crystals of 

 which it very closely resembled. Upon this conviction I pre- 

 scribed for her, but desiring her to leave the vessel with its 

 contents, till a convenient opportunity for examining them. 

 The urine had been passed in the morning about an hour or 

 two before it was brought to me, and, in the course of the day, 

 I commenced the examination. Having poured the urine off, 

 the sand was found collected together in a small mass at the 

 bottom of the cup. A small quantity being placed upon char- 

 coal, and urged with the blowpipe, presented a scoriaceous 

 appearance, without consuming or leaving the white ash usually 

 left by lithic acid. Reddened litmus paper, being moistened 

 and brought in contact with it, indicated no alkaline re-agency. 

 A small quantity was now placed in a small glass capsule, and 

 a drop of nitric acid being placed upon it, it was heated. An 

 effervescence took place, but on continuing the heat till the 

 acid was dissipated, the dried mass presented nearly the same 

 appearance as before the experiment. On being exposed to 

 the vapour of ammonia, there was a slight indication of the 

 presence of lithic acid interspersed through the mass. I now 

 examined it with a small magnifying glass, and perceived that 

 it consisted of small angular crystals, transparent, some colour- 

 less like quartz, others of an ambery or topaz colour, and 

 having a certain degree of refractive density. On treating 

 them with caustic potass *, and then washing them, nearly the 



* Silica is soluble in the caustic fixed alkalies ; but it is not very sen- 

 sibly affected by the liq. potassae of the shops, unless the silica be in a 

 state of minute mechanical division, and after a prolonged digestion. 

 The lithic acid, on the contrary, is very speedily taken up by this 



