RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



A study of humus in Hawaiian soils, W. P. Kelley and W. McGeobge 

 {Hawaii Sta. Press Bui. 33, pp. 23, fig. 1). — While studying Hawaiian soils as 

 regards their humus content It was found that those soils obtained from the 

 upper islands, which had a varied physical structure and in some instances a 

 high percentage of clay and silt, gave unreliable results with the official method. 

 As the clay in these soils could not be removed by any other means than by 

 using the Cameron-Breazeale-Alway clay filter method (E. S. R., 24, p. 9), the 

 authors made an effort to overcome the difficulties which attend its use. 



This was done by drawing the solution through the filter in the reverse direc- 

 tion from that usually employed. For the compression chamber was substi- 

 tuted an ordinary suction pump. "The tube of glazed porcelain, attached to 

 the lower end of an S-in. Pasteur-Chamberland tube, was broken off so as to 

 leave this end of the tube open; then the tube was inserted into the upper 

 opening of a bell jar, such as is used for filtering with suction, in a manner 

 similar to that employed in the use of a Gooch. A large part of the tube was 

 allowed to extend into the filtering jar and the connection was made air-tight by 

 means of a short piece of Gooch tubing or a rubber stopper. It was also found 

 desirable to coat the upper portion of the tube with paraffin so as to prevent the 

 passage of the solution except in the lower half of the filter tube, otherwise 

 the solution will pass down the side of the bell jar. 



"A 50 cc. aliquot of humus solution (the preliminary extractions with hydro- 

 chloric acid were made by digesting 10 gm. of soil in 200 cc. of fifth-normal 

 hydrochloric acid at ordinary laboratory temperature for 5 hours, filtering, 

 and washing free from acid with distilled water, as outlined by Fraps in his 

 directions for cooperative study of humus determination for the Association 

 of Official Agricultural Chemists, May, 1911), which represented 1 gm. of soil, 

 was drawn through the tube by means of reduced pressure, the filtrate being 

 collected in a short cylinder. After the entire aliquot was drawn through, a 

 4 per cent solution of ammonia was then passed through so long as it showed 

 any color. Usually about 200 cc. was required. In no instance was it found 

 necessary to use more than 250 cc. The filtrate and washings were then evapo- 

 rated to dryness and the determinations completed as usual. 



" Some difficulty was experienced in completely removing the clay in certain 

 soils. There was found to be considerable difference in different tubes in this 

 respect. Some filters will remove all clay, while others seem to allow a small 

 amount of the most finely divided clay to pass through. . . . 



" The time required to complete a filtration was found to be about 3i hours, 

 and by arranging a number of filtering jars in a series an ordinary Richardson 

 pump will provide suction for at least 3 filters, and with close-fitting con- 



50696"— No. 1—12 2 7 



