280 Scientific Intelligence. 



sorbed, it may give out to the air. The enormous quantity of impure 

 matter filtering from all parts of a large town into its many natural 

 and artificial outlets, does at first view present us with a terrible picture 

 of our underground sources of water. But when we examine the soil 

 of a town we do not find the state of matters to present that exaggerated 

 character which we might suppose. The sand at the Chelsea Water- 

 works contains only T43 per cent, of organic matter after being used 

 for weeks. In 1827, Liebig found nitrates in twelve wells in Giessen, 

 but none in wells two or three hundred yards from the town. Dr. 

 Smith has examined thirty wells in Manchester, and he finds nitrates 

 in them all. Many contained a surprising quantity and were very nau- 

 seous. The examination of various wells in the metropolis showed 

 the constant formation of nitric acid ; and in many wells an enormous 

 quantity was detected. It was discovered that all organic matter, in 

 filtrating through the soil, was very rapidly oxydized. The presence 

 of the nitrates in the London water prevents the formation of any 

 vegetable matter ; no vegetation can be detected, even by a micro- $ 



scope, after a long period. The Thames water has been examined 

 from near its source to the metropolis, and an increasing amount of 

 impurity detected. In the summary to this Report, Dr. Smith states 

 that the pollution of air in crowded rooms is really owing to organic 

 matter and not merely carbonic acid ; that all the water of great towns 

 contains organic matter; that water purifies itself from organic matter 

 in various ways, but particularly by converting it into nitrates, — that 

 water can never stand long with advantage unless on a large scale, and 

 should be used when collected or as soon as filtered. 



11. On the Manufacture of Ice. — Ice at the present day is con- 

 sidered one of the necessaries rather than one of the luxuries of 

 life. Unfortunately those parts of our country where it is most needed 

 are without the means of regular supply. The inland portions of the 

 southern and south-western States, do not get the benefit of the ice trade 

 from the north, the natural ice crop is precarious or altogether want- 

 ing, while the heat of summer untempered by the sea breeze makes 

 ice one of the greatest comforts of life. 



The manufacture of ice is therefore likely to become a great desid- 

 eratum and already much has been said on this subject in the papers. 

 It appears that some plan has been devised although no description of 

 the process has been published. As much that is erroneous has been 

 stated, we have thought it worth while to give the results of an actual 

 trial of well known methods. 



In France, freezers are used for making ice, ice creams, &c, by the 

 use of several frigorific mixtures, and these freezers are probably to be 

 met with in several of our larger cities. Two different forms have 

 been exposed for sale in the city of New York. The mixtures most 

 recommended for use are crystallized sulphate of soda drenched with 

 muriatic acid, or nitre salammoniac and water. The former of these 

 would in most places be a costly mixture, and while unsafe in careless 

 hands, and destructive to the vessels likely to be used, could not be 

 employed without loss, as it would be impossible to recover the acid 

 when the solution was evaporated. The solution of nitre and salam- 

 moniac is liable to none of the objections — the salts are not costly, and 





