386 Dr. E. W, Davy on a new and simple Method of 



their execution much time and trouble, and in some cases com- 

 pHcated and expensive apparatus; and though capable in ex- 

 perienced hands of yielding tolerably accurate results, would in 

 the case of those not much practised in chemical manipulation, 

 and perhaps unaware of the many sources of error to be guarded 

 against, give anything but correct results, and are therefore in- 

 applicable to the greater number of those desirous of a quick 

 and easy method of determining the quantity of urea in urine. 



The method I propose is one of extreme simplicity, and can 

 be performed by almost any one in a very few minutes, and is 

 capable of yielding results sufficiently accurate for all practical 

 purposes. It is founded on the fact I have recently observed, 

 that urea is very readily decomposed by the chlorides, or rather 

 hypochlorites of soda, potash or lime; and its constituent 

 nitrogen is evolved in the gaseous state, and from the quantity 

 of gas evolved I estimate the amount of urea present. 



After trying different means of carrying out that fact with a 

 view of making it available to determine the quantity of urea in 

 urine, I found that the following veiy simple one seemed to 

 answer the purpose completely. I take a strong glass tube, 

 about 12 or 14 inches long, closed at one end, and its open 

 extremity ground smooth, and having the bore not larger than 

 the thumb can conveniently cover. This I fill more than a third 

 full of mercuiy, and afterwards pour in carefidly a measured 

 quantity of urine to be examined, which may be from a quarter 

 of a drachm to a drachm or upwards, according to the capacity 

 of the tube; then holcUng the tube in one hand near its open ex- 

 tremity, and having the thumb in readiness to cover the aperture, 

 I quickly fill it completely full with a solution of the hypochlorite 

 of soda (taking care not to overflow the tube), and then instantly 

 cover the opening tightly with the thumb, and having rapidly 

 inverted the tube once or twice to mix the m-ine with the hypo- 

 chlorite, I finally open the tube under a saturated solution of 

 common salt in water, contained in a steady cup or small mortar. 

 The mercury then flows out and the solution of salt takes its 

 place, and the mixture of urine and hypochlorite being lighter 

 than the solution of salt, will remain in the upper part of the 

 tube, and will therefore be prevented from descending and mixing 

 with the fluid in the cup. A rapid disengagement of minute 

 globules of gas soon takes place in the mixture in the upper part 

 of the tube, and the gas is there retained and collected. The 

 tube is then left in the upright position till there is no further 

 appearance of minute globules of gas being formed, the time 

 being dependent on the strength of the hyjDochlorite and the 

 quantity of urea present; but the decomposition is generally 

 completed in from three to four hours ; it may, however, be left 



