S6 



SIXTH REPORT — 1836. 



Ehrenberg*, in his journey into Siberia, observed a rose-red 

 colour in the salt lake Elton, in the steppe of Astracan, which 

 did not appear to belong to the water, but faded on drying ; and 

 I perceive in a recent journal, that Mr. Pajean, in his travels 

 in Tuscany, remarked that the red substance, which is produced 

 on the surface of water charged with marine salt in that country, 

 is the result of an accumulation of an enormous quantity of 

 small Crustacea, of one or two lines in length, having nearly the 

 form of a craw-fish, which live very well in brine of 15 degrees, 

 but die when the water is further concentrated. 



It is stated, that M. Darcet brought similar Crustacea from 

 certain lakes in Egypt which are charged with natron. 



With respect to the blue colour sometimes observed in rock- 

 salt, it is possible that the same kind of explanation may apply 

 to it. I was once inclined to imagine, that it might be caused by 

 a compound of iodine with some vegetable principle, analogous 

 to starch, or producing with the former a siiiiihirly coloui-ed 

 compound ; but I could detect no iodine in the specimen, and 

 failed to reproduce the violet tinge, when the salt had been dis- 

 solved in water and crystallized a second time. 



Now Ehrenberg relates, that a lake in the South of Prussia 

 in 1819, produced a particular colouring matter very similar to 

 indigo, which appeared to be of a vegetable nature ; and Scores- 

 byt mentions, having in 1820 observed, that the water of the 

 Greenland sea was chequered with alternate green and blue 

 stripes, and that these colours were produced by minute animal- 

 cules of the medusa kind. 



Gases 

 evolved 

 from 

 springs. 



Carbonic 

 acid. 



The gases disengaged from mineral waters have been investi- 

 gated by Bischoff, Anglada, Boussingault, Longchamp, and 

 others. 



BoussingaultJ remarks, that the elastic vapours which rise so 

 abundantly from the thermal springs of the Andes, consist of 

 carbonic acid and sulphuretted hydrogen, and the same observa- 

 tion applies to most of those in connexion with volcanic forma- 

 tions elscM'here. 



Of these two gases, the one most copiously evolved is carbonic 

 acid, which, as is well known, produces those extensive deposits 

 of calc-sinter, that are so common in caverns exposed to the 

 drippings of water, and of arragonite§, which are of rather rarer 



* On Blood-red Water. t ylrctic Researches. 



X Edinburgh New PhiloxophiculJournal, vol. xv. 151. 



§ See a pajjcr in the Annales de Chimie, June, 1834, on the presence of Ar- 

 ragonitc in an Artesian well at Tours. I possess some also deposited from the 

 spring of St. Nectaire in Auvergne. 



