P OP ULAR MIS CELL ANY. 



717 



mildest wmters and the warmest summers, 

 must be looked for where the land approach- 

 es the thirty-fifth parallel, at the southern 

 points of Spain, Sicily, and Crete. The 

 highest known mean in Europe is at Cata- 

 nia, 65', the temperature of January being 

 there 51, and that of August 81. Gibral- 

 tar enjoys a warmer temperature in January, 

 54, nearly corresponding with the tempera- 

 ture of Cairo. The January of Catania is 

 like that of the end of April, the January 

 of Gibraltar like that of the first half of 

 May, in Berlin. These extreme southern 

 points suffer, however, occasionally from 

 frost and snow. Snow fell on the African 

 coast in 1845 and 1850, and in the latter 

 year a temperature below the freezing-point 

 was observed as far south as the Sahara ; 

 and the Nile is said to have been frozen in 

 the year 859. So it is safe to assume that 

 no place in Europe is secure from snow and 

 frost. 



A New Theory of Chemical Affinity. 



M. Berthelot has endeavored, in his recently 

 published " Essai de Mecanique Chimique 

 fondee sur la Thermochimie," to connect the 

 laws of chemistry and the theory of the 

 unity of physical forces. He believes that 

 he has discovered a direct relation between 

 chemical affinity and the capacity of differ- 

 ent bodies in combining to throw off heat. 

 Thus hydrogen burns in oxygen, liberating 

 enormous quantities of heat ; the affinity of 

 the two bodies is known to be strong. The 

 same is the case with phosphorus and oxy- 

 gen. But nitrogen and hydrogen, instead 

 of liberating heat when they combine, ab- 

 sorb it. Their affinity for each other is fee- 

 ble. Again, when two bodies combine in 

 different proportions, forming different com- 

 pounds, it is always the combination in which 

 the most heat is liberated that tends to form. 

 More heat is liberated in the formation of 

 water than of the binoxide of hydrogen, and 

 it is water that is naturally formed when the 

 bodies burn together. This law of chemical 

 compositions and decompositions has been 

 termed by M. Berthelot the princijyJc of max- 

 imum work, and is enunciated by him thus : 

 Every chemical change accomplished with- 

 out intervention of a foreign energy (heat, 

 electricity, light) tends to the production of 

 the body or system of bodies which liberates 



heat. This principle throws light on a mul- 

 titude of facts hitherto unexplained. M. 

 Berthelot indicates many applications of his 

 principle. Acetic acid, combining with soda, 

 produces a certain amount of heat, and forms 

 acetate of soda ; hydrochloric acid, combin- 

 ing with soda, liberates more heat, and forms 

 chloride of sodium. If, now, we apply hy- 

 drochloric acid to the acetate of soda, chlo- 

 ride of sodium will be formed, with the pro- 

 duction of an amount of heat just equal to 

 the difference between the heat of formation 

 of acetate of soda and that of chloride of 

 sodium ; but the converse will not take place 

 when acetic acid is mixed with chloride of 

 sodium. Combinations which are formed 

 with much liberation of heat are very sta- 

 ble ; those in which heat is not liberated 

 are unstable. Chloride of sodium will resist 

 a white heat without decomposing, while 

 chloride of nitrogen, in the formation of 

 which heat is absorbed, will decompose and 

 explode spontaneously. This fact leads to 

 another remark: that, in accordance with 

 the law of maximum work, all explosive 

 bodies are bodies that produce heat in being 

 decomposed. 



Diseases of Miners. Dr. Paul Fabre, of 

 Commentry, France, has made a particular 

 study of the diseases of miners. He has 

 found that diseases, the character of which 

 is largely governed by certain accessory cir- 

 cumstances, are prevalent among workmen 

 who labor in damp or wet galleries. No 

 morbid symptom is developed among those 

 who work in a gallery which is simply damp 

 and of a temperature of not more than 58. 

 But if cold water falls upon them, or if they 

 have to put their legs in water, they become 

 subject to lumbago, sciatica, to indefinite 

 pains in their limbs, and often to a real 

 rheumatism. The rheumatism is generally 

 subacute, sometimes chronic, and most often 

 localized in a single joint generally that of 

 the left knee, on which the pick-men and 

 heavers rest in working. In galleries which 

 are saturated with moisture and where the 

 temperature exceeds 77 to 86, the work- 

 men are soon overcome with an extreme 

 lassitude; they get hot, they gasp for 

 breath, the sweat rolls down their bodies, 

 and they are obliged to stop working and 

 rest for a while in a cooler spot, A rapid 



