AS INDICATED BY OSMOMETERS. 73 



Where absorption rates were maintained, they appear clearly to 

 indicate the moisture content and the water-supplying power. The 

 5 per cent sample could supply water to the absorbing surface at a rate 

 of 0.03 c.c. per hour per 10 sq. cm. of area; the 10 per cent samples could 

 supply moisture to the osmometer at an hourly rate of 0.08 or 0.09 c.c; 

 and the firmly packed 20 per cent sample maintained a rate of 0.14 c.c. 



On the other hand, the data for the soils which did not exhibit 

 maintained rates fail to give any real indication as to the maximum 

 possible rates at which these soils might supply water; in these cases 

 it appears clearly that a marked and progressive drying of the soil 

 near the absorbing surface has entered into the dynamics of the 

 system, and that this drying might have been wholly or partially 

 avoided had a less concentrated sugar solution been employed. Thus, 

 for example, we dare not assert that the 25 per cent soil sample might 

 not have maintained a rate as high as 0.39 c.c. if the initial rate had 

 been lower, through the use of a weaker solution as absorbent. It is 

 true that this same consideration may apply, in a much less marked 

 degree, to the soil mixtures which did exhibit maintained rates. If the 

 osmometric method here introduced becomes available for physiologi- 

 cal and ecological measurements, lower concentrations will need to be 

 studied. To some considerations of the probable nature and effects of the 

 drying out of the soil layer next the absorbing surface we shall turn in 

 a later paragraph. 



OSMOMETER B. 

 WATER AND SOIL TESTS WITH OSMOMETER B. 



This instrument had an effective area of 8.35 sq. cm. and a coefficient 

 of correction of 1.198. It was tested against water and operated 

 against soil mixtures in a manner quite similar to that used in the case 

 of instrument A. The details of these tests bring out no more than 

 has been shown by the details already presented and they will therefore 

 be suppressed here. It is expedient, also, to present the data for water 

 and soil tests together. 



The average hourly rates, together with their means, for two similar 

 tests with water, and for one test with 25 per cent, two tests with 

 20 per cent, and one test with 15 per cent soil, will be considered. The 

 temperatures for these tests were of similar range, from about 27.5° to 

 about 31° C, and all tests will be here regarded as comparable in this 

 regard. The averages for all these experiments are set forth together 

 in table 10. The final means represent the rates after the first hour, 

 instead of after the second, as in the preceding case. 



Table 10 shows the results of these water tests to be in good agree- 

 ment with each other and with those from the first two similar tests 

 with osmometer A. This means that instrument B had practically 

 the same water-absorbing power per unit of area as had instrument A. 



