222 AGRICULTURAL ANALYSIS 



In experiments made in the laboratory of the Division of Chem- 

 istry in testing for loss on ignition, we have uniformly found 

 that natural mineral phosphates will lose from nearly one to 2.5 

 times as much on ignition as a basic slag which has been kept 

 for two years. A basic slag in the laboratory more than two 

 years old gave, as loss on ignition, 4.12 per cent. Several sam- 

 ples of finely ground Florida phosphates gave the following per- 

 centages of loss on ignition, as compared with a sample of slag: 



Odorless phosphate (slag), 4.12. 



Florida phosphates, 8.06, 6.90, 9.58, 6.40, 10.38 and 10.67, re- 

 spectively. 



There are some mineral phosphates, however, which are ig- 

 nited before being sent to the market. We have had one such sam- 

 ple in the laboratory from Florida which gave, on ignition, a loss 

 of only 1.4 per cent. In this case it is seen that the application of 

 the process of ignition would not discriminate between a basic 

 slag and a mineral phosphate. 



It may often be of interest to know what part of the loss, on 

 ignition, is due to loosely held water in form of moisture. In 

 such cases the sample should first be dried to constant weight 

 and then ignited. In the following data are found the results 

 obtained with samples treated as above indicated and also ignited 

 directly. Number one is a basic slag two years old and the others 

 are Florida phosphates. 



Heated to 100 C. then ignited. Ignited directly. 



I.oss at JyOss on Total I.oss on 



100 C. ignition. loss. ignition. 



No. i (Slap) 2.57 1.77 4.34 4.12 



No. 2 (Rock) 2.61 5.19 7.80 8.06 



No. 3 " 1.09 5.77 6.86 6.90 



No. 4 " 0.42 9.20 9.62 9.58 



No. 5 " 1.81 4.83 6.64 6.40 



No. 6 " 4.36 6.52 10.88 10.83 



No. 7 " 3.31 7.01 10.32 10.67 



(6) Presence of. Snlfids. Another point noticed in the labora- 

 tory of the Division of Chemistry is that the basic slags uniformly 

 contain sulfids which are decomposed upon the addition of an 

 acid with an evolution of hydrogen sulfid. 



(7) Presence of Fluorin. In applying the test for fluorin, it 

 has been uniformly found here, that the mineral phosphates respond 



