Simplified qualitative chemical analysis for urinary calculi.

OXALATE Stone powder (2-3 mg) is moistened on an ordinary glass slide with two to three drops of 20% nitric acid and is slowly heated over a small flame to dryness and then for a further 5-10 seconds but without charring. The following results may be noticed: (a) formation of a conspicuous reddish-brown froth indicating ammonium urate; (b) formation ofa flat purplish-brown layer, evidence of uric acid. (Energetic oxidation of uric acid by heat and nitric acid decomposes the intermediate split-product alloxanthin sufficiently for the evaporating ammonia to produce at least partly the characteristic purple coloured murexide, the ammonium salt of purpuric acid); (c) total combustion, except for a small charred sticky part, often accompanied by a disagreeable smell-evidence of cystine; (d) a greyish-white layer, indicating oxalate, phosphate or both; (e) a whitish-green layer, evidence of xanthine. Addition of potassium hydroxide produces a brilliant red colour; (f) whatever the outcome of the procedure with heat and nitricacid,theresidueon the slide is still fit for