92 Mr. H. Russell's Description of a Pressure Gauge. 



The fuel used at the pans for the last process is partly 

 ■wood, and partly anthracite from the neighbouring moun- 

 tains. The anthracite answers remarkably well when once 

 ignited, as it preserves for a long time a regular degree of 

 heat. The consumption of wood was formerly so great that 

 it has denuded many of the higher mountains in the Taren- 

 taise, and exposed' them to the action of the atmosphere, 

 which has occasioned vast eboulements ■■; for it is found that 

 forests are of the greatest utility, in preserving precipitous 

 mountains from destruction. The fact is now so well ascer- 

 tained, that the Government, for this cause alone, has lately 

 paid particular attention to the preservation of the wood. The 

 quantity of salt made here annually, is estimated at 100,000 

 myriagrammes, or about 2,250,000 lbs. avoirdupois, and about 

 9000 myriagrammes of sulphate of soda, or about 187,000lbs. 

 The other alkaline matter which adheres to the pans is sold 

 to the glass-makers. The Government receives, on the aver- 

 age, 150,000 francs for the products, out of which it is esti- 

 mated that 30,000 are expended for wood and fuel, 8000 for 

 materials employed in the buildings, and for the faggots &c, 

 and 62,000 for the wages and the salaries of the different 

 officers, leaving an annual profit of 50,000 francs. In some 

 of the mountains of the Tarentaise, the gypsum is intermixed 

 with rock salt en masse, and was worked by the peasants ; but 

 the places are now closed up, and so strictly guarded by or- 

 der of the Government, that I found it difficult to procure 

 specimens. 



These mines were formerly worked, the salt being sepa- 

 rated from the gypsum by solution, and subsequently evapo- 

 rated by fire ; but the great eboulements, caused by clearing 

 away the wood from the sides of the mountains, obliged the 

 Government to abandon the mines, and undertake the manu- 

 facture of salt at the Salines. These mines are mentioned by 

 the Roman historians. 



XVII. Description of a Pressure Gauge recommended for its 

 Simplicity of' Construct ion and Principle; with Observations 

 on the Gauge proposed by Mr. Seaward*. By Mr. Henry 

 Russell. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 A N examination of the instrument proposed by Mr. Sea- 

 ■^ ward, and described by him in your Magazine, No. 309, at 

 pages 36 and following, has induced me to lay before your 



* See p. 36 of this volume. 



notice 



