Diazo-

(di-a'-zo-). In chemistry, a prefix signifying that a compound contains phenyl, united with a radical consisting of two nitrogen atoms. D.-acid, one of certain volatile liquids of yellow color and peculiar odor, which distil undecomposed with steam or under reduced pre ure. They are slightly soluble in water, but mix readily with alcohol and with ether. D. -compound, in chemistry a compound containing a group consisting of phenyl united with a radical consisting of two nitrogen-atoms (whence the name). D. -reaction or test, a urinary test, originally thought to be especially valuable in the diagnosis of enteric fever. It is not found in the urine of healthy persons. The test is made by mixing 200 parts of sulphanilic acid solution (concentrated solution in water) with io parts of pure hydrochloric acid, and 6 parts of nitrite of sodium solution. To this mixture add an equal volume of urine with sufficient ammonia to render the whole alkaline. A bright or carmin-red denotes the reaction. See Tests, Table of.