Vol. XXIII. No. 4.] 



POPULAE SCIENCE NEWS. 



53 



It is still a matter of doubt whether the sponge 

 should be classified with the animal or the vegetable 

 world. But the most accurate scientific observers, 

 as Dr. Saunderson, Mr. Huxley, Dr. Poggiola, Mr. 

 Ruskin, and others, are collecting and recording 

 new phenomena constantly which tend to throw 

 light on this much-vexed question. 



SCIENTIFIC BREVITIES. 



The Force of a Ray of Light. — It is some- 

 times asserted that the unit of work — the erg — is too 

 small to be of any use, but Prof Langley has shown 

 that the perception of the color crimson, is produced 

 by an expenditure of energy upon the retina, which 

 can be represented by 10— !•' horse-power, or 0001 

 of an erg; while the sensation of green is due to 

 O'oooooooi of an erg. 



Practical Cljenjistry aijd tlje ^rts. 



[Original in The Popular Science Neun.] 



SOME OF THE CONSTITUENTS OF DRINK- 

 ING WATER AND THEIR MEANING. 



BY 



PROFS. PETER T. AUSTEN, PH. D., F. C. S., 



AND 



FRANCIS A. WILDER, M. S. 



PART II. 



HARDNESS. 



Water containing salts of lime and magnesia does 

 not at first yield a lather with soap, but " kills" the 

 soap. Such water is called "hard." If the lime 

 and magnesia are present in the form of carbonates, 

 they are thrown down when the water is boiled, 

 since the carbonic acid gas, which, when dissolved 



^ o,.!,.^ LLC ..aiuuiiic aciu gas, wnicn, wnen dissolved 



Electricity for Snakes.-A report comes by ,-„ the water, imparts to it the property to dissolve 



way of Germany that a novel use of electricity has 

 been made in India, for the prevention of the intru- 

 sion of snakes into dwellings. Before all the doors 

 and around the house two wires are laid, connected 

 with an induction apparatus. Should a snake 

 attempt to crawl over the wires, he receives a shock 

 of electricity, which either kills or frightens him 

 jnto a hasty retreat. 



Motion at Rest.— An exceedingly interesting 

 illustration of the phenomenon of "motion at rest" 

 was recently exhibited before the Royal Insti- 

 tution. London, the demonstration being so com- 

 plete that small letters placed on a disk, revolving 

 several thousand times a minute, were seen and read 

 with entire distinctness. The accomplishment of 

 this unique result was brought about by means of 

 an electrical arrangement, which caused brilliant 

 sparks to illuminate the print at the exact instant 

 only when the type was vertical. But for the buz- 

 zing produced by the great velocity of the disk, the 

 words would have been supposed to be entirely at 

 rest. This application of the electric spark, of 

 course, gives a ready means of observing any and all 

 changes which may take place in either matter or 

 machinery in rapid motion. 



Cloid Photography. —At the meeting of the 

 Royal Meteorological Society, Dr. A. Riggenbach, 

 of Basle, read an interesting paper on a method of 

 photographing cirrus clouds. Great difficulty is ex- 

 perienced in obtaining photographs of cirrus clouds, 

 the reason being that the blue light of the sky acts 

 with nearly the same activic energy as the white light 

 of the clouds on the sensitive silver salts of the 

 plate. What is wanted is that this blue light of the 

 sky should be dulled, the light of the clouds being 

 left unafiected, and this can be done by means of 

 the analyzer of a polarizing apparatus. The light 

 from the blue sky is partly polarized, and to the larg- 

 est extent at the points which are situated 90° from 

 the sun ; the plane of polarization passing through 

 the points looked at, the sun, and the eye of the ob- 

 server. On the other hand, the light coming from 

 a cloud is only polarized to a slight extent. If an 

 obsidian plate be placed before the lens of a photo- 

 graphic camera, so that its plane is inclined at an 

 . angle of 33° to the optical axis of the lens, and the 

 camera be placed so that the sun's rays shine per- 

 pendicularly on one of its sides, we then turn the 

 whole apparatus around, in the direction in which 

 the sun lies, as an axis, until a cirrus cloud is visi- 

 ble in the camera. If a sensitized plate be inserted, 

 a picture of the cloud can be produced under the 

 most favorable conditions possible. A still simpler 

 mode of obtaining such cloud pictures is to use the 

 surface of a lake as a polarizing mirror. The best 

 clouds for such a purpose are at sunrise or sunset, 

 at an altitude of about 37", and in an azimuth either 

 greater or less than that of the sun by 90*^. 



the carbonates of lime and magnesia, is driven off 

 by the boiling. The dissolving agent being thus 

 removed, the carbonates of lime and magnesia pre- 

 cipitate, and the water is rendered softer. Advan- 

 tage is taken of this in the preliminary heating of 

 water before its introduction into steam boilers. 

 Hardness which is removed by boiling is called 

 " temporary" hardness. If the hardness consists of 

 sulphates or chlorides of lime and magnesia, or of 

 any other salts or substances which kill soap and 

 which are not removed by boiling, the hardness is 

 called "permanent." 



Hardness is usually expressed by stating the num- 

 ber of grains per gallon of carbonate of lime 

 (chalk), or substances equivalent in soap-killing 

 power, that are contained in a gallon of the water. 

 The ettect of the hardness of water in increasing the 

 cost of using it, may be best estimated by calculating 

 that each degree of hardness causes the "destruc- 

 tion of 12 pounds of the best hard soap by every 

 10,000 gallons of water." 



The effect of a considerable amount of lime and 

 magnesia salts on the human system is not constant, 

 since entirely opposite effects are produced in differ- 

 ent people. Some medical writers catalogue a long 

 list of ailments as caused by the use of hard waters. 

 There seems, however, to be no doubt but that the 

 solvent action of water, and its power to remove the 

 wastes of the human organism, increases with its 

 freedom from mineral substances in solution. 

 Hence the less the hardness, the better adapted will 

 it be for drinking. As before stated, the opinion is 

 growing now very rapidly that water is drank for the 

 sake of the water in it, and not for anything else. 

 Modern scientific investigation indicates that in 

 proportion as the amount of pure water supplied to 

 a community increases, there is a corresponding 

 but far greater decrea.se in the death rate, the disease- 

 factor, the cost of living and of manufacturing, 

 while with the increase in the supply of pure water, 

 increases also, in a most surprisingly rapid manner, 

 the thrift, morality, and degree of civilization. The 

 amount of water used per head by the inhabitants 

 of a community is a very fair index of their state of 

 civilization. It is a matter of regret that so much 

 timidity is evinced in dealing with questions of 

 water-supply. There are many thousands of deaths 

 in cities that might be prevented by an improve- 

 ment in the water-supplies. The death rate of the 

 United States at present is estimated to be over 

 100,000 per year too high. 



oxygen required to oxidize organic matter. 

 This determination indicates relatively the amount 

 of very easily oxidizable organic matter present in a 

 water. Alone, it does not possess a very definite 

 interpretation, but, in conjunction with the other 

 determinations, it is of value in forming an opinion 

 as to the conditions of the water. In time, it may 



be possible to give the determination a greater im- 

 portance, especially if in any way by its use we 

 shall become able to tell the difference between liv- 

 ing and dead organic matter. 



dissolved gases. 



All natural waters dissolve from the air certain 

 amounts of oxygen and nitrogen gases. If the 

 water is perfectly free from organic matter, the 

 ratio of dissolved gases would not alter very much, 

 but if organic matter is present, more or less of the 

 oxygen is consumed in oxidizing and destroying it. 

 This consumption of oxygen may be direct, or it may 

 be brought about through the agency of minute or- 

 ganisms, which require oxygen for their existence, 

 and which, in turn, feed upon the organic matter. 

 The nitrogen which is dissolved in the water does 

 not suffer much change, but the oxygen, from the 

 causes just explained, fluctuates to a marked extent. 

 As one of the principal products of the oxidation of 

 organic matter is carbonic acid, water in which or- 

 ganic matter has suftered oxidation, usually shows 

 an increased amount of dissolved carbonic acid gas 

 and a decreased amount of dissolved oxygen. A 

 water may, therefore, be bright and sparkling, and 

 still be anything but pure. The higher the content 

 of dissolved oxygen, and lower that of dissolved 

 carbonic acid gas, the better the water is to be con- 

 sidered. 



COLOR. 

 The opinions of chemists concerning the condi- 

 tions indicated by the color of a water are well ex- 

 pressed by Dr. Fox, as follows : 



"It is helpful in forming an opinion as to the 

 quality of a water to pay a certain regard to its 

 color, although apart from other indications of its 

 conditions, no reliance should be placed on this test. 

 Speaking generally, it may be said that waters of 

 great purity exhibit a bluish hue, that waters pol- 

 luted by filth have various shades of a straw or 

 brownish tint, deeper in proportion to the amount 

 which they contain, whilst peaty waters generally 

 display a nutty-brown color. To this rule there are 

 many exceptions. A water may possess a strong 

 brown or yellowish tint, and yet be free from filth, 

 e. g., some peaty waters, and waters containing 

 iron. Certain artesian waters of great purity have 

 a straw tint. The Loch Kathrine water, which sup- 

 plies the city of Glasgow, displays a color apparent 

 to every one. On the other hand, some waters that 

 are devoid of color as distilled water, and exhibit a 

 greater brilliancy, are found to be polluted with a 

 large amount of animal filth. A water mav be 

 almost colorless, and yet exhibit on analysis much 

 vegetable matter, e. g., the water-supply of Bourne- 

 mouth. A water may be colorless, and still contain 

 peat, for white peat is occasionally met with, which 

 's a form of incompletely carbonized vegetable mat- 

 ter. Practically, however, peaty waters present 

 various shades of a brownish olive-green c»lor, if 

 the peaty matter is in larger quantity, through a 

 nutty-brown to a coffee color, when the peat is old 

 and abundant." 

 And again : 



"Thousands are still to be found who believe that 

 if a water is bright and clear, and not unpleasant to 

 the taste, it must be good ; whilst it has been proved, 

 over and over again, that such a water may be pol- 

 luted with unspeakable filth, and that an excessive 

 brilliancy of a water is a suspicious sign." 



The properties which a water should possess to 

 render it acceptable for drinking, household, and 

 manufacturing purpo.ses, and, conversely, the prop- 

 erties which will render it unfit for the uses to which 

 the water-supply of a city is intended, are about as 

 follows : 



For drinking purposes, a water should be clear, 



