26 SOME ASPECTS OF THE INDIGO INDUSTRY IN BIHAR 
to the aspirator. The flow of the gas was regulated by means of the screw 
clip D and was kept at about 3 litres per hour. Before opening the tap T 
ail the connections were tested for leakage. On opening the tap T, soil gas 
passes through the baryta solution which absorbs the CO2, forming barium 
carbonate. The three perforated silver cones, a, b and c in the tower of the 
Reiset’s apparatus allow complete absorption of the CO by the baryta solu- 
tion. About 10 litres of soil gas were aspirated in each case. At the end of 
each experiment, the volume of gas and the temperature (indicated in the 
thermometer in the neck of the aspirator bottle) were noted, the tap T was 
closed, and the apparatus disconnected and brought to the laboratory. The 
baryta water from the Reiset’s apparatus was filtered quickly, filled into a 
burette, a measured portion run out and titrated against standard acid. The 
strength of the baryta water used was determined once previous to the aspi- 
ration of soil gas and the difference in strength after aspiration gave the 
measure for calculating the amount of COz contained in the soil gas. By this 
method, the amounts of CO, in the soil gas from (1) grassed down, (2) grassed 
down but partially aerated by trenches and (3) cultivated plots, were deter- 
mined once every month and the results obtained are given in Table II and 
Plate I. 
Results. 
The results at once show that the CO2 has been consistently high in the 
grassed plot and low in the surface cultivated plot ; the trenched plot being 
intermediate between the two as regards CO, content. During the first three 
months, January to March, whereas the grassed plot had shown practically no 
improvement, the other two showed a marked falling off in the COz present 
with the lowering of the water-level. During May and June, when the weather 
was hottest and when the water-level was its lowest, the CO. content in all 
the three plots was also lowest. With the advent of the monsoon and a fair 
amount of rainfall, all the plots showed a considerable rise in the amount of 
CO, present in the soil gas-——the increase being about four times as much in 
grassed and trenched plots, and one and a half times as much in the cultivated 
plot. From July to September, coincident with the increase in rainfall and 
the consequént rise of the water-level, there has been’ a regular rise in the 
amount of CO, in the soil gas from all three plots. The October and Noy- 
ember figures show a marked fall in the amount of CO, in all three plots. 
November 17th, 1919. JATINDRA NATH MUKHERJEE, 
First Assistant to the Imperial 
Agricultural Chemist, Pusa. 
