IODIN Ifr PHOSPHATES 273 



calcium fluorid in a fossil bone in a phosphate from the Charles- 

 ton deposits. Gabriel has suggested a means of determining 

 a minimum limit of fluorin in bones and teeth by the develop- 

 ment of etchings in comparison with known quantities of pure 

 calcium fluorid. The minimum quantity of calcium fluorid neces- 

 sary to produce a distinct etching, in known conditions, having 

 been determined, the test is applied to known weights of ignited 

 bone or teeth. He concludes from his results that the ash of 

 bones and teeth often contains less than one-tenth per cent, of 

 fluorin. Since, however, there is a loss of fluorin from calcium 

 fluorid on ignition, the whole of the fluorin may not have been 

 available in the tests described. 



234. lodin in Phosphates. The presence of iodin has been de- 

 tected in many natural phosphates and is of interest in the dis- 

 cussion of the problem of their origin. 83 A sample of phosphate 

 from Florida was found to contain 0.014 per cent, of iodin. This 

 element has also been observed in the phosphates from other lo- 

 calities, as has been shown by Gilbert. A qualitative test for 

 the detection of iodin may be applied in the following manner : 

 Some finely ground phosphate is mixed with strong sulfuric acid 

 and the gases arising from the reaction are aspired into some 

 carbon disulfid or chloroform. The violet coloration arising 

 indicates the presence of iodin. The gases carrying the iodin 

 may also be brought into contact with starch-paste producing 

 the well known blue color. 



The quantity of iodin present in a phosphate is rarely more 

 than one or two-tenths of one per cent. It can be determined as 

 a silver salt, in the absence of chlorin or by any of the standard 

 methods found in works on quantitative analysis. 



Iodin is quite a constant constituent of Florida phosphates. 

 For a quantitative determination, the sample is treated with an 

 excess of strong sulfuric acid in a closed flask and during the 

 decomposition a stream of air is aspired through the flask and 

 caused to bubble through absorption bulbs containing sodium or 

 potassium hydroxid in solution. 



The temperature of the decomposition may be raised to about 

 200. After the distillation is complete the sodium iodid formed 

 81 L'Engrais, 1895, 10 : 65. 



