ADULTERATION OF PHOSPHATIC SLAGS 221 



Schucht recommends the following method of procedure. 78 

 One gram of the slag, finely ground, is treated in a beaker glass 

 with about 150 cubic centimeters of Jensch's citric acid solution 

 .and warmed for 12 hours in an air-bath at from 50 to 70 

 with frequent shaking. Afterwards it is diluted with 100 cubic 

 centimeters of water, boiled for one minute and filtered. The 

 filter is washed thoroughly with hot water and the phosphoric 

 acid is estimated in the filtrate in the usual way. With artificial 

 mixtures of basic slags and other phosphates, the quantity of basic 

 slag can be determined by the above method. 



(4) Method of Wrampelmeyer. According to Wrampelmeyer, 

 the most convenient method for discovering the adulteration of 

 basic slag is the use of the microscope. 79 All finely ground nat- 

 ural phosphates are light colored and with a strong magnifica- 

 tion, appear as rounded masses. In basic slags the particles are 

 mostly black, but there are often found red-colored fragments 

 having sharp angles, which retract the light in a peculiar way, 

 so that, with a very little experience, they can be recognized as 

 being distinctive marks of pure basic slag. 



In artificial mixtures of these two phosphates, which we have 

 made in the laboratory of the Division of Chemistry, we have been 

 able to detect with certainty as little as one per cent, of added 

 mineral phosphate. 



One form of adulterating natural mineral phosphates has been 

 mixing them with finely pulverized charcoal or soot to give them 

 the black appearance characteristic of the basic slags. This 

 form of adulteration is at once disclosed by simple ignition or by 

 microscopic examination. 



(5) Loss on Ignition. If all doubts cannot be removed by the 

 use of the microscope, the loss on ignition should be estimated. 

 Natural phosphates all give a high loss on ignition, ranging from 

 eight to 24 per cent., while a basic slag gives only a very slight 

 loss on ignition, especially when fresh. A basic slag which has 

 stood for a long while and absorbed carbon dioxid and moisture, 

 may give a loss on ignition approximating, in a maximum case, 

 the minimum loss on ignition from a natural phosphate. 



78 Zeitschrift fiir angewandte Chetnie, 1890, 3 : 594- 



79 Die landwirtschaftlichen Versuchs-Stationen, 1894, 43 : 183. 



