Sept. 19, 1884.] 



♦ KNOWLEDGE ♦ 



241 



rendered possible. Speaking of the observation of the 

 temperature, he stated that the lowest temperature ever 

 recorded was experienced in February last, when the mean 

 temperature was 50 deg. below zero. 



AlIERICAX TEGETATIOX. 



Among the most interesting papers read before the 

 British Association, at Montreal, was one by Prof. Asa 

 Gray, on the " Characteristic Features of North American 

 Vegetation." He said that when the British Association 

 met for the first time on this side of the ocean, it was not 

 to be wondered at that a corresponding member of the 

 association for a quarter of a century should be present to 

 read a paper to the naturalists of Section D. lie presented 

 certain outlines of the flora of Canada and the United 

 States as distinct from those in England or the Atlantic 

 coast. The first impression made upon a visitor would be 

 the similarity to the flora of England, many of the plants 

 being almost the same. As one proceeds westward and 

 southward, the difllerences become more marked. While 

 an agricultural people displaced the aborigines of New 

 England, the flora of Europe also gradually supplanted the 

 plants of the red man. Many of the common plants of 

 the Old World sprang up in the farms, and fields, and 

 roadsides as civilisation proceeded. At almost every step in 

 America the English botanist meets with well-known plants 

 which have found their way from American to English 

 soil. The Virginia creeper, rhododendron, and other well- 

 known plants in England are of American origin. Turning 

 from similarities to diflerences, an observant botanist on 

 the Atlantic coast would be struck by the liberal number 

 of trees and shrubs to be seen in this section of the country 

 in comparison with England or Scandinavia. The wealth 

 of this flora is an obvious one. The most interesting con- 

 trast between the eastern section of the American continent 

 and Europe is the large number of tropical flowers which 

 the heat of the American summer permits to grow in 

 northern latitudes. There are also in this section many of 

 the Arctic plants which remained behind after the glacial 

 period had passed away ; the same plants are also to be 

 found in Japan and China, but are wholly wanting in 

 Europe. Europe was at one time much similar to Green- 

 land, which is now undergoing a period of extreme glacia- 

 tion fatal to flora. In Europe also the glacial period had 

 destroyed many types of flora which had escaped in 

 America. The Arctic flora of America is significant ; a 

 few species are found on the cool shores of Lake Superior, 

 the shores of Labrador, and certain mountain summits in 

 the Appalachian mountains. 



THE INTERNATIONAL HEALTH 

 EXHIBITION. 



XVI.— WATER AND WATER-SUPPLIES— (co»(»n«ed). 



IN conclusion of our remarks upon the supply of water 

 for domestic purposes, we now propose to give a few 

 simple directions for the benefit of those of our readers 

 who may desire to test their drinking water, so as to be 

 able to decide for themselves whether it is wholesome or 

 unwholesome. 



In collecting a sample for scrutiny, one ought to be ex- 

 tremely careful to thoroughly cleanse the vessel used in 

 gathering. A medium-sized glass test-tube or beaker, re- 

 peatedly washed, at least three times, with pure distilled 

 water, obtainable from any chemist, may be taken as 



chemically clean. The sample of water placed in this test- 

 tube ought to be colourless, and free from floating particles, 

 however minute ; otherwise it must be regarded as unsuit- 

 able. Our senses would probably pronounce the water scath- 

 less, and yet it may be highly impure. Its harmful qualities 

 usually arise from the nature of the soil through which it 

 has passed, and the reservoirs, if any, in which it has 

 been detained. It is further liable to be contaminated 

 by its passage along delivery-pipes and its storage in cis- 

 terns ; hence we find that amongst the injurious products 

 which it may take up, a few are more prevalent than 

 others, and, indeed, are regarded exclusively as the sources 

 of annoyance to the householder. Of these, the presence 

 of — (f() Dissolved or other organic matter in undue pro- 

 portions may at once be detected by the use of W^anklyn's 

 standard solution of permanganate of potash and potash. 

 Add one or two drops to a test-tube full of the water ; if 

 the violet colour of the reagent remains unchanged except in 

 intensity, and does not throw down any sediment even after 

 a lapse of about twelve hours, the water may be looked 

 upon as free from organic matter. If the water is only 

 slightly contaminated, the violet hue will disappear 

 gradually, but foul water will change the violet imme- 

 diately into a faintly perceptible yellowish brown. The 

 ordinary permanganate test, however, is apt to be vitiated 

 by tlie presence of harmless nitrous acid, or protoxides of 

 iron, to which it gives up oxygen as readily as it does to 

 albuminoid organic matters. The water ought not there- 

 fore to be condemned solely after this test, although it 

 may with justice be looked upon with suspicion, (p) The 

 presence of lead dissolved from service-pipes, especially by 

 waters from non-calcareous regions, may be immediately 

 detected by the addition of one or two drops of a solution 

 of ammonium sulphide to a test-tube full of the water ; 

 lead poisoned water will instantly turn brown or dirty in 

 colour ; good water will merely diminish the intensity of 

 the yellow ammonium sulphide, (y) Excess of iron may 

 be demonstrated by the addition of a few drops of a solu- 

 tion of ferrocyanide of potassium, by which the water will 

 become greenish-blue, more or less markedly according to 

 the degree of contamination, (c) Too much lime in solu- 

 tion can be shown by the addition of a drop of ammoniac 

 oxalate, when a dense white precipitate will follow. Of 

 course, the less lime there is the less will resultant milki- 

 ness be. Ammoniate oxalate also precipitates strontium 

 and barium from solutions, but as these substances do not 

 usually occur in drinking waters they may be disregarded. 



All the above-mentioned tests may be carried out by any 

 person of ordinary intelligence,* and will suffice to show 

 the character of the water-supply, and enable the house- 

 holder to take precautionary measures, if necessary. In 

 all cases, however, where the tests given fail to satisfy the 

 consumer, or to create a suspicion that his supply is un- 

 wholesome, we would strongly recommend him to call in 

 the assistance of an analyst, and to apply to the company 

 or supplier for redress. We have shown, in our considera- 

 tion of the subject of filtration, how extremely bad water 

 may be rendered wholesome ; let us hope that those of our 

 readers who are interested in this question, upon which the 

 welfare of thousands of their fellow-beings depends, may be 

 induced to try the few experiments we have just noted, to 

 test their own drinking-water, and, if they find it defective, 

 to select one of the types of filter we have described, to see 

 what it will do for them. We shall be glad to hear of and 

 report their results in future. 



* Mr. Maignen, of 22 and 23, Great Tower-street, E.G., supplies 

 a hox containing test-tabes, re-agents, and directions, for this 

 purpose. 



