Distribution of Iodine. 285 



(!()nsideriug that whilst one or two grammes of soil, taken 

 from the hills and terraces in the neighbourhood of Paris, 

 or from the fields of Brie, of Beauce, of Bourbonnais, or of 

 Bourgogne, suffice incontrovertibly to prove the presence of 

 iodine, we must, generally, in order to obtain a correspond- 

 ing result,*^operate upon double the weight of the soil of La 

 Bresse or of the plain of Turin, and upon ten times the weight 

 of the arable soil of Tarentaise, of Maurienne, and of the 

 Valley of Aoste. It is a circumstance worthy of remark, that 

 in the same district, reddish or ferruginous and clayey soils 

 are more impregnated with iodine than white or bituminous 

 and quartzose schist soils. I shall mention, as an example, 

 the Valley of Graisivaudan, of which the yellow and rather 

 stiff soil of the right bank resemble those of Bresse and the 

 neighbourhood of Alexandria, while the black and light soil 

 of the left bank are similar to those of the high valleys of 

 Isere and of Arc. 



The temperature of the water has a very great influence 

 over its dissolving power of the compounds of iodine con- 

 tained in the soil. Thus the schistous soil of the Alps, which 

 does not yield an appreciable quantity of the iodurets to water 

 of a temperature lower than + 10 degrees centigrade, sup- 

 plies a very sensible proportion at from + 20 to 50 degrees 

 centigrade. At 100 degrees centigrade, one pint (litre) of 

 water can often extract from 10 grammes of this earth enough 

 of iodine to bring it to the state of good drinkable water. 

 The scarcity of the iodurets in the waters of the Alps, then, 

 is explained, not solely by the state of the atmosphere, but 

 also by the low temperature of the streams. It is highly 

 probable that, previous to the greater part of the iodine which 

 the pluvial waters yielded, the soil of the Alps had long fur- 

 nished it ; and possibly it may be the truth that the goitre 

 and cretinism have only become endemic in those countries 

 since this principle has become exhausted. 



The presence of a certain proportion of carbonate of potash 

 or of soda in water destined to extract the iodine from the 

 soil renders them more soluble : this addition is also abso- 

 lutely necessary for fixing iodine, when we operate at a high 



