In April 1938 I published a method for the determination of carbon in soils (Alper, 1938). This method consists of digesting the soil with a mixture of sulphuric acid and potassium bichromate, passing the products of combustion through a heated combustion tube and absorbing the carbon dioxide produced in barium hydroxide. Digestion and absorption take place in a closed system which allows neither the escape nor entrance of carbon dioxide. The absorption flask is evacuated and separated from the digestion flask by a glass tap. During the process of digestion, as the pressure in the system increases, this tap is manipulated, allowing the escape of gas into the absorption flask. A pressure gauge in the system indicates when the tap should be opened.

The sensitivity of this mercury pressure gauge causes some difficulty in technique. It is necessary to watch the experiment throughout the digestion and to manipulate the tap constantly. In order to obviate this difficulty an improvement in the apparatus has been effected. The pressure gauge has been replaced by an elastic bladder (a child's balloon serves the purpose admirably) which is connected to the system by means of a glass ┬-piece. At the commencement of the experiment the pressure within the system is slightly less than atmospheric owing to the suction of CO2-free air through the apparatus. This causes the complete deflation of the balloon. As digestion continues the balloon becomes distended. The distension of the balloon must not be allowed to go too far as too great a pressure in the system will result in losses through leakage.