ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 247 



winter; the chlorides were much less in summer than in winter. The 

 average of sulphates in a certain period of thirteen months was 0.004, 

 of chlorides 0.0033. Seven samples collected near Horsham, in Sussex, 

 gave sulphates 0.0048, chlorides 0.0041. A sample collected on Dart- 

 moor during a gale from the southwest gave the following results: 

 Sulphates 0.0005, chlorides 0.0087. Proximity to the sea evidently 

 increases the chlorides and reduces the sulphates. At St. Bartholomew's 

 Hospital, in central London, the sulphates were 0.0388, the chlorides 

 0.0179, and the amounts were greater in summer than in winter. The 

 quantities of these impurities in the air of a large town are much above 

 the average of the country. The rain does not give acid reaction, but 

 wherever it is contaminated with soot it becomes distinctly acid after a 

 few hours. Soot, then, being acid and becoming moistened by rain, 

 must play an important part in the corrosion of buildings and other 

 materials on which it has been deposited. Experiments were made by 

 Dr. Eussell by means of a conical vessel filled with ice, to ascertain the 

 amounts of impurities condensed from air in London. The results were 

 remarkable,- sulphates 0.1344, chlorides 0.0506, ammonia 0.006; and in 

 fogs the amounts were 0.2480 sulphates, 0.1215 chlorides. 



ARSENIOTJS ACID IN RAIN. 



A gallon of rain in the city of London has been found to contain 

 0.00021 grain of arsenious acid. 



AMMONIA IN THE AIH. 



Ammonia is always present in the air in minute traces, either free or 

 combined. It is a chemical compound of 14 parts by weight of nitro- 

 gen and 3 of hydrogen, and arises from the decomposition of organic 

 matter. It is lighter than air in the proportion of 8.5 to 11.47. Although 

 the quantity rarely exceeds 3£ parts in 10,000,000 of air, this is suffi- 

 cient to be of very high importance to the growth of vegetation, for the 

 gas is soluble to quite an extraordinary amount in water, and is thus 

 continually being brought down from the atmosphere in rain and dew. 

 Brandes found, by evaporation of rain, in each million kilograms from 

 8 (May) to 65 (January) kilograms of residue, of which ammonia 

 salts formed a considerable portion. 1 Bain, according to Boussingault, 

 contains about three-fourths of a milligram of ammonia per liter, equal 

 to 7 kilograms per hectare per annum. Dew contains about 6 milli- 

 grams, equal to about 29 kilograms per hectare per annum; fog, about 

 50 milligrams, and in Paris, 138 milligrams. Water dissolves from 

 700 to 1,000 times its volume of ammonia, according to the temperature. 

 Bepresenting the quantity of ammonia in rain at Valentia, in Western 

 Ireland, by 1, the quantity inland in England was 5.94, at Glasgow 

 50.55. The albuminoid ammonia was: Yalentia 1, Manchester 7.38, 

 London 6.23. 



1 Pierre. 



