7H 



THE POPULAR SCIENCE MONTHLY. 



pelf-purification takes place only if the water 

 has not been previously sterilized by boil- 

 ing, and protected afterward against the 

 entrance of germs. But if a sterilized water 

 has been subsequently exposed to the air or 

 mixed with ordinary water, it undergoes the 

 same changes as waters that have not been 

 sterilized ; its oxidizable power and its am- 

 monia decrease, while nitrous or nitric acid 

 is formed. If, therefore, the development 

 of organisms in the water is rendered im- 

 possible, self-purification is also impossible. 

 Direct oxidation by atmospheric oxygen cer- 

 tainly docs not take place ; and, if ozone and 

 hydrogen peroxide play a part, it is a sub- 

 ordinate one. The kind of living beings 

 which effect the purification of waters will 

 differ greatly according to circumstances. 

 Such a change of species has actually been 

 observed in one and the same water-course 

 in the different stages of its pollution. Self- 

 purification may take place, even when in- 

 dustrial refuse is allowed to flow into the 

 water in addition to organic pollution. Dr. 

 J. Soyka has made experiments on the pow- 

 er of the soil to absorb poisonous substances 

 and destroy them ; and has showed it to ex- 

 ist in the cases of strychnine and a consid- 

 erable number of the organic alkaloids. His 

 experiments have not been extended to the 

 ptomaines. Nevertheless, we must beware of 

 supposing that the treatment of foul waters 

 can safely be left to Nature. Where the 

 supply of polluting matter is continuous in 

 time and space, natural purifying agencies 

 fail. An important lesson to be learned 

 from the researches of Emich and Soyka is, 

 that the microbes, both of earth and water, 

 are not all to be regarded as disease-gen- 

 erators. On the contrary, certain kinds of 

 them are converting malignant matter into 

 forms in which it is harmless, or even use- 

 ful. Hence, it is at least possible that, in 

 the application of disinfectants or "germi- 

 cides," there is room for discretion. 



School Life and Health.— Dr. Thomas 

 Whiteside Iline, of Bradford, England, has 

 made inquiries into the effect of school life 

 upon the mortality of children, taking as 

 the basis of his conclusions the reports of 

 deaths among children of from five to fif- 

 teen years old, persons of that range of 

 ages being regarded as probably those upon 



whom the effects of school life and work 

 would be most marked. Comparing the 

 returns from 1871 to 1880 with those from 

 1861 to 1870, he finds that while the mor- 

 tality of children from all causes and from 

 zymotic diseases — on which school influ- 

 ences are negative — has considerably di- 

 minished, their mortality from nervous dis- 

 eases — the direction in which school influ- 

 ences would be most felt — has exceptionally 

 remained stationary. To this he adds that 

 the figures for 1881 and 1882 likewise show 

 identical results in both instances. Further 

 than' this, he finds that there has been an 

 improvement in the death-rate from nerv- 

 ous affections among children below five 

 years, who are out of school, or have been 

 in it for only a short time. Yet the whole 

 of the mischief must not be attributed to 

 the effect of schooling alone ; but, as all the 

 world lives faster than it did, the nervous 

 system of children is likewise stimulated at 

 the present day to an extent unknown a 

 generation ago, and greatly to their disad- 

 vantage. The existence of such sources of 

 mischief in the habits of the day supplies 

 a strong reason why all school influences 

 calculated to enhance the mischief should 

 be removed. 



Seasoning Timber. — Of the common sense 

 of the question of seasoning timber, Mr. 

 Thomas Blashill says, in an address on the 

 general subject : " Wood must not be dried 

 so quickly that it will be made unsound by 

 cracks. It must not be dried so much that 

 it will absorb fresh moisture when it comes 

 into the atmosphere in which it has perma- 

 nently to remain. It is not merely a ques- 

 tion of time, but of judgment, the objecta 

 being to see that the timber is gradually re- 

 duced in scantling as it dries, and so treated 

 in temperature and stacking that it neither 

 splits nor gets out of shape. ... To sum up 

 the whole class of questions connected with 

 seasoning, we want timber that will not 

 shrink after it is brought into use, that will 

 not work or twist out of shape, will not de- 

 cay through damp, and will not be destroyed 

 by insects. Wood may also be indurated, 

 that being the result of polishing and of 

 varnishing to some extent. Upon the whole, 

 it is desirable to encourage all means of 

 treating wood so that it may possess some 



