TRANSACTIONS OF THE SECTIONS. 583 



Mr. Lowe conceived that this artificial mode of producing 

 the bisulphuret of iron, in crystals, would be an interesting 

 fact to the geologist, as affording some confirmation of the 

 igneous origin of trap rocks, in reference especially to the 

 observation made by Professor Sedgwick and Mr. Murchison, 

 that rocks of an aluminous nature are often found at the point 

 of contact with basaltic matter, to be not only indurated, but 

 to contain crystals of pyrites. 



He also showed upon a portion of a worn-out cast iron 

 retort numerous octahedral crystals of protoxide of iron, 

 the effect of long-continued heat. Good specimens of these 

 crystals are very rare, now that only the best iron, and 

 that of the second melting, is used in the gas-works to which 

 Mr. Lowe is attached. A wrought iron bolt, which had been 

 for many hours acted upon by steam, at a bright red heat, 

 presented a crystallized surface. 



Mr. Lowe likewise laid before the Section specimens of pure 

 Prussian blue, and of blue and green pigment, obtained from 

 the refuse lime-water of gas-works. 



This refuse was for many years allowed to run to waste into 

 the river Thames ; of late it has been evaporated under 

 the bars of the fui'naces, and passed, partly decomposed, up the 

 chimney. It may now he rendered available for a more useful 

 purpose. 



On the quantity of Carbonic Acid in the Atmosphere. By 

 Henry Hough Watson. Communicated by Dr. Dalton. 



At the commencement of his undertaking, the author con- 

 fined his experiments principally to the quantity of carbonic 

 acid in the atmosphere of the town of Bolton ; and then, to 

 arrive at the difference in quality between an atmosphere in 

 its natural purity and one like that of Bolton, which we know 

 to be artificially impregnated, he fixed upon Horrocks Moor, 

 a situation three miles north-west of the town of Bolton, and 

 elevated, as he had found by barometrical observation, about 

 584 feet above it ; and made the remainder of his experiments 

 upon air received at this place, except that thrice during the 

 course of his investigation he operated upon air received on 

 the top of Winter Hill. 



Winter Hill is situate from five to six miles north-west of 

 Bolton, and about a mile north-east of the well-known Rivington 

 Pike ; its height above Bolton is about 1211 feet. 



The author gives his first experiment as an example of his 

 method of analysis. A bottle capable of holding 1 88 •400 grains of 



