ua 



Scientific Proceedings, Royal Dublin Society. 



Table III. 



Comparison of centripuged and filtered soil extracts. Soil, one part ; water, five parts. 

 Total volume about 25 c.c. ; time of extraction, eighteen hours. 



* Still turbid, but fit to examine. 



t Clear, slightly yellow. 



X Peat 1, water 6; peat on paper. 



J No. 17 diluted with equal volume of distilled 

 water. 



In the above table both methods agree well with some soils, whereas in 

 others, No. 4 and No. 17 for example, wide discrepancies appear. Thus No. 17 

 is changed pFO-QS namely, almost a tenfold reduction in acidity, hy filtering 

 through unextracted and pH 025 through extracted paper. On the other hand, 

 No. 63 has its alkalinity much reduced by using acid-extracted paper. 



Table IV. 



Effect op filtration on pU op peat extract. 



Sample. 

 17 



17B 



Do. 

 Do. 



Composition. 



10 grms. peat, 60 e.e. water 



Liquid drained oS from 



No. 17, ISO e.e. distilled 



water added to residue 



Uo. do. 



Do. 



do. 



■pU. 

 4-5.5 

 4-95 



5-25 

 5-02 



Notes. 



Centrifuged. 

 Do. 



1st 80 c.c. of filtrate, Munktell 's 



No. 0. 

 2nd SO e.e. of filtrate. 



In Table IV are shown the results of an attempt to satisfy the acid- 

 ahsorbing power of the acid-extracted paper by making the fii'st filtrate very 

 large. The latter here shows an error of pH Oo, whereas in the second it is 

 only pH 007. The error may thus be much lessened by the rejection of a 

 large first filtrate. 



The differences between various filter-papers is shown in Table V, which 

 records pH values ascertained approximately by spot tests using the usual 

 indicators, all of which were tried on each j^aper with concordant results. 

 The values about pH '^■4^S are probably less accurate than the others, since 

 methyl red is in many respects not so reliable as are indicators of the sulplione 

 phthalein series. 



