224 AGRICULTURAL ANALYSIS 



From the above data it is seen that the solvent action of water 

 especially would be of value, inasmuch as it dissolves only a mere 

 trace of the mineral phosphates, approximating one per cent, of 

 the amount dissolved from basic slag. In the case of the citric 

 acid it is found that the amount of materials soluble in this sol- 

 vent for basic slag is fully four times as great as for the mineral 

 phosphates. Both of these processes, therefore, have considera- 

 ble value for discriminating between the pure and adulterated 

 article of basic slag. 



(9) Specific Gravity. The estimation of the specific gravity 

 is also a good indication for judging of the purity of the slag. 

 This is best done by weighing directly a given volume. Basic 

 slag will have a specific gravity of about 1.9, while natural phos- 

 phates will have about 1.6. 



(10) Conclusions. From the above resume of the standard 

 methods which are in use for determining the adulteration of 

 basic slag, it is seen that there are many cases in which grave 

 doubt might exist even after the careful application of all the 

 methods mentioned. If we had only to consider the adulteration 

 of basic slag with certain of the mineral phosphates, that is, tri- 

 calcium phosphate, the problem would be an easy one, but when 

 we add to this the fact that iron and aluminum phosphates are 

 employed in the adulteration, and that artificial slags may be so 

 used, the question becomes more involved. 



Of the single tests, examination with the microscope appears 

 to be the most fruitful. 



In doubtful cases, one after another of the methods should be 

 applied until there is no doubt whatever of the judgment which 

 should be rendered. 



DETERMINATION OF OTHER CONSTITUENTS IN 

 NATURAL PHOSPHATES 



194. Water and Organic Matters. The sample used for deter- 

 mining water and organic matters, according to the practice of 

 Chatard, should be ground fine enough to leave no residue on 

 an 80 mesh sieve, and should be thoroughly mixed by passing it 

 three times through a 40 mesh sieve. 81 



81 Transactions of the American Institute of Mining Engineers, 1892-93, 

 21 : 165. 



