43 6 
THOMPSON YATES LABORATORIES REPORT 
The shape and arrangement are best illustrated by the above diagram. It is necessary 
also to be provided with a rubber stopper valve of the ' Allenbury ' feeding bottle 
(value 4d.), which fits into the opening in the upper zone of the pearshaped bulb as 
seen above. Also a pipette to hold at least 5 c.c, for introducing and withdrawing the 
hypobromite solution before and after an estimation and cleansing the bulb. 
Having charged with hypobromite solution, insert the stopper with the notch on the 
rim pointing downwards, for that corresponds with the position of the slit seen in the 
diagram, which admits the urine and acts as a valve to prevent escape of the nitrogen, 
and adjust so that the level of the coloured fluid rises to the first mark on the graduated 
tube (not the first number). This is most easily done by injecting air by means of 
the syringe. The urine is then projected on to the surface of the hypobromite 
solution through the slit seen in the diagram of the stopper by means of an ordinary 
vulcanite glass hyperdermic syringe. The nozzle of the syringe ought to fit with a 
fair amount of tightness into the opening of the stopper, which, being of india-rubber, 
is adaptable. Push the piston of the syringe slowly inwards, and the urine escapes 
quite easily on to the surface of the solution inside, and having withdrawn the syringe 
and the fingers from the bulb rotate the instrument gently from side to side, catching 
hold by the arch above. // is thus not necessary to touch the bulb containing the mixture 
evolving the gas after the urine has been introduced. The rotary movement gives the 
requisite amount of shaking to liberate all the nitrogen speedily. Then leave for a 
minute or more to cool, or if time be an object, rotate again to see that no more gas 
is given off, and the coloured fluid in the graduated tube no longer rises, and cool by 
means of a cold wet ra£. Then read off. 
This gives the volume of nitrogen in c.cs. for 1 c.c. of urine. From that it is easy 
to deduce the urea. There is, of course, a slight error in volume owing to the extra 
pressure of the column of fluid (distilled water with three drops of red ink) in the 
graduated tube. The extent of this error may be estimated thus and is so small that 
for ordinary purposes it may be neglected. 
Suppose the volume of nitrogen read off" for 1 c.c. of urine is 8 c.c. Measuring 
the difference between the level of the fluid in the tube and that in the bulb we find 
it say nine centimetres which, of course, means that the pressure on the gas in the 
bulbs exceeds the atmospheric pressure at the moment by nine centimetres of water. 
Then, according to Boyle's law, the volume of a gas varies inversely with the 
pressure. Air and nitrogen are almost equally compressible, so that the mixture 
may be calculated for as if it were only one gas. Thus, if V = correct reading and 
V, = reading as given by Nitrometer, and P = atmospheric pressure in c.c. of water. 
P, = pressure on mixture of gases = (P + 9) in c.c. of water. 
... 1 V, orV (?L±9) = 8- ( IQ 33 + 9\ = 1336 
P, P VP/ V 1033 / 1033 
= 8*07 or an error of a fraction of a cubic millimetre. 
