144 Prof. J. Emerson-Reynolds on the 



{411}, {6 11}, {711}, UO, 11}, and {2 3 3} were found in 

 alternate octants only, and are consequently hemihedral. The 

 faces of {3 2 1} were for the most part badly developed, and 

 did not permit of any certain conclusion being drawn. Hes- 

 senberg found a plane of the form in each of two adjacent 

 octants which excludes a hemihedrism with inclined faces. I 

 believe it, from my observations, to be holohedral. A farther 

 examination of such crystals as are to be found in the various 

 collections might possibly set the question of the hemihedrism 

 of the mineral at rest, and would certainly be interesting. 



XX. Short Reports from the Chemical Laboratory of Trinity 

 College, Dublin. By J. Emerson-Reynolds, M.D., Pro- 

 fessor of Chemistry, University of Dublin *. 



No. 5. On the Rapid Estimation of Urea. 



A DISTINGUISHED physician, who wished to make 

 frequent determinations of the urea daily excreted bv 

 a patient, requested me to devise a method which would enable 

 him to make the desired estimation — (a) rapidly, (b) with suf- 

 ficient accuracy for ordinary clinical purposes, (c) with simple 

 and easily constructed apparatus, and (cl) without the use of a 

 balance or of any measuring-vessels other than the fluid-ounce 

 and minim measures which a medical man is in the habit of 

 employing. 



This interesting practical problem was solved in the manner 

 I shall presently describe ; and the results obtained by the use 

 of the method devised have been so satisfactory as to lead me 

 to expect that it may be found generally useful where a high 

 degree of accuracy is not desired. 



I propose, however, before concluding this paper, to describe 

 a less simple plan for the estimation of urea than that just 

 referred to, but one which is capable of affording results of 

 greater precision. 



In both the methods mentioned I take advantage of the now 

 well-known reaction of sodic hypobromite with urea. When 

 a strongly alkaline solution of sodic hypobromite is added to 

 a liquid containing urea, the latter suffers rapid decomposition 

 into water, carbonic anhydride, and pure nitrogen gas. The 

 carbonic anhydride is not evolved as gas, but is absorbed, with 

 formation of sodic carbonate, by the free alkali of the liquid 

 used to effect decomposition ; the nitrogen is evolved in the 

 gaseous condition, and its bulk determined either indirectly or 



* From the Scientific Proceedings of the Eojal Dublin Society. Com- 

 municated by the Author. 



