ELISHA MITCHELL SCIENTIFIC SOCIETY. 45 



and filtering from silica. The silica was also in each case deter- 

 mined. The amount precipitated was 50 c. c. of the solution, and 

 the same four solutions were used that were compared with the 

 Philadelphia method in the last eight comparative results cited, 

 (Table II.) 



I. 2. 3. 4- 



Four solutions with silica gave 11.70 14.12 13-52 ii.ig(a.) 



Four solutions with silica removed 11.52 13.61 11-55 io.3o(b.) 



Difference .iS .51 1.97 .8g 



SiOo found 1.16 2.02 2.96 2.26 



It is impossible to tell how far the differences between (a) and (b) 

 are due to unavoidable loss incident upon two evaporations to dry- 

 ness and extended manipulation, but the fact will be noticed at once 

 that the differences in each case vary directly as the amount of silica 

 found, but being in no case as much as the silica found. Strange to 

 say also, if the presence of the silica tended to increase the per cent, 

 of the PaOs found, then there ought to be equally as much silica in 

 the other four solutions from the Philadelphia method (Table II), 

 because the per centageshere of PgO^ are not materially greater than 

 the per cents there, in fact, within the limits of error. I am inclined 

 to the opinion that the presence of silica in large amounts is hurtful, 

 but that if a fusion is carried only far enough to completely destroy 

 all organic matter and reduce the fused mass to a homogeneous 

 state and no farther, not enough silica is brought into the solution 

 to do any harm — certainly very little more than is in an ordinary 

 acid solution, such as is gotten by the Philadelphia method. For 

 here are four fusion solutions showing practically the same per cents 

 of PaOs as four Philadelphia method solutions, and yet showing 

 silica present in each case, and a diminution in per cent P-^Os when 

 silica is removed. I therefore conclude that if proper precautions 

 are taken not to fuse unnecessarily long, the fusion method is in- 

 comparably preferable to the Philadelphia method. Nor do I 

 believe, from the results of the first set of experiments (Table I), 

 that the Philadelphia method in many cases sufficiently oxidizes and 

 destroys organic matter. 



One more time-consuming objection to the Philadelphia method, 

 inadvertently omitted above, T will mention here. Most copious and 

 protracted washing of the yellow " phospho-molybdate of ammo- 

 nia " with ammonium nitrate solution is necessary, in order to free 

 it from the magnesium chloride which is formed when the MgO 

 (after the ignition) is dissolved in HCl. Unless this is entirely 



