26o 



NATURE 



[JULY I ::, 1S94 



rain in falling washes the air from a large proportion of the sus- 

 pended organic matters inseparable from a crowded city, and 

 also from the unburnt particles of carbon, which incomplete 

 combustion allows to escape from our chimneys ; and charged 

 with these, it still collects more dirt of various kinds from the 

 roofs of our houses, and finally finds its way into our water-butts 

 as the semi-putrid sludge which often causes the true-bred 

 cockney to wonder "if this so-called purest form of natural 

 water is so foul, what on earth must the other forms of water be 

 like?" If in the counir)- the rain waier is collected and siored 

 in suitable reservoirs, then we have (he most perfect water that 

 can be obtained for washing and cleansing purposes. 



In some kinds of water collected under what we might con- 

 sider ideal circumstances, we find "a something" which acts 

 as a check upon the cleansing action of the soap. 



In Attica, close to Athens, on the slopes of Mount Pentilicus, 

 the Emperor Hadrian built some huge marble underground 

 aqueducts to collect and lead the rain water down as a supply 

 for Athens, the whole w.iter-shed consisting of marble ; this 

 mountain being justly celebrated as the source from which the 

 finest statuary marble is obtained. Here, falling through the 

 clear southern air on to a collecting ground lormed of the 

 material which all ages have considered the most suitable for 

 baths and reservoirs, one would expect the water to be like the 

 pure rainwater, absolutely free from dissolved solid impurities, 

 and one of the best waters of its kind for washing purposes ; 

 yet not only does it waste a large amount of soap before a 

 lather is obtained, but if we examine the channels through 

 which it has for centuries flowed down to the valley, we find 

 that it has formed a heavy deposit, which collecting unchecked 

 through long ages, has all but choked up the once spacious 

 passages. A piece of this deposit I have obtained through 

 the kindness of a friend, and on analysis it proves to be : — 



Calcic carbonate 



Silica... ... 



Organic matter 



Moisture 



It is, in fact, a natural incrustation deposited by the water, and 

 a similar action is seen in the formation of stalactites in many 

 caverns, through the roof of which water charged with certain 

 calcareous compounds has slowly found its way. 



In the passage of the rain through the air small quantities of 

 carbon dioxide or carbonic acid gas are dissolved from the 

 atmosphere, whilst in slowly percolating through the surface 

 soil on which it has fallen the water is brought in contact in the 

 pores of the soil with far larger volumes of this gas, which is 

 being continually generated there by the decomposing vege- 

 tation and other organic matter in a state of decay. Under 

 these circumstances the water becomes highly charged with the 

 gcs, and sinks on through the ground until it comes in contact 

 with some impermeable strata through which it cannot pene- 

 trate, and here it collects until a sufficient head of water has 

 been formed for it to force its way along the strata to the surface 

 of the earth, where it now appears as a spring, and during this 

 pai'Sage through the earth it has dissolved everything that will 

 yield 10 its own solvent action or to the activity of the carbon 

 dioxide, which dissolved in water forms the weak carbonic 

 acid, a compound which will dissolve many substances insoluble 

 in the water itself, such as calcic carbonate, occurring in the 

 soil as mnr> I" i"— 'one, or chalk, and also the carbonates of 

 iron and If we examine a spring water, we shall 



fin'i that r I impurities can be divided into two classes : 



for instance, taking the Kent water supplied at Greenwich, 

 and obtained from deep wclU in the ch.ilk, we find its saline 

 conuiluents in grains per gallon are : — 



Calcic carlionate .. 

 Calcic tulphaic 

 Magnetic sulphate 

 Magnetic nitrate 

 Swiic chloride 

 Sodic nitrate 

 Silica, alumina, &c. 



i6'3o 

 5-37 

 093 



I '20 

 2 '64 

 I '21 



o'97 



And of these the calcic sulphate, magnesium, and sodium salts 

 are diuolved by the solvent action of the water in the same 

 way that sugar would be, whilst the chief impurity, calcic 



NO. 1289. VOL. 50] 



carbonate, is scarcely at all soluble in the water itself, 16,000 

 parts of pure water only dissolving one part of the carbonate, 

 but is readily soluble in the carbonic acid, in the water 

 which converts it into soluble calcic bicarbonate. 



In the household, waters are roughly classified as hard or soft 

 waters, and the property of hardness manifests itself, as a rule, 

 to the householder by its action upon soap, and also by the 

 amount of " fur " which it causes in the kettle, these actions 

 being due to calcic bicarbonate, calcic sulphate, and the 

 magnesium salts present in it, all of which act upon soap and 

 cause it to curd instead of forming a lather by converting the 

 soluble sodic ole,ite and stearate into insoluble lime salts, 

 whilst the bicarbonate by decomposing and depositing " chalk " 

 causes the fur. 



A more careful examination, however, reveals the fact that 

 this property of hardness owes its origin to two different causes, 

 for if we boil water until all the bicarbonate is broken up and 

 the calcic carbonate deposited, the clear water left behind it is 

 still hard, though to a far less extent, and will still decompose 

 a certain proportion of soap. The hardness which cm be got 

 rid of by boiling is due to bicarbonate of lime, and some- 

 times also bicarbonate of m.ignesia, and is called '" temporary 

 hardness," whilst the hardness left after boiling the water is 

 due to calcic sulphate and the soluble magnesium sulphate, 

 chloride and nitrate, and is called " permanent hardness." 



The relative hardness of waters is estimated by the amount 

 of soap they will destroy, i.e. convert from the form of soluble 

 sodic oleate and stearate into the condition of insoluble 

 oleales and stearates of lime, and one grain of calcic 

 carbonate or its equivalent in sulphate or salts of magnesia 

 dissolved in a gallon of water, is said to equal 1° of hardness. 



The sample of Kent water of which an analysis has been 

 given, contains 23 '6 grains of these salts, and would be said 

 to have nearly 24 hardness, 7 '5 of which would be permanent 

 and 1 6 "3 temporar)*. 



When it is considered that 1° of hardness in water will waste 

 10 grains of soap per gallon of water used, we become aware 

 of the economic importance of the kind of water employed in 

 the household, a gallon of the Kent water, for instance, using 

 up 236 grains or nearly half an ounce of soap before any becomes 

 available to form a lather and exert a cleansing action upon 

 the skin. 



Glasgow used to have a hard water service, and when this 

 was discontinued and the soft Loch Katrine water was supplied 

 in its place, it made a difference of several thousands a year in 

 the money expended in soap. 



From these facts it is manifest that a soft water supply is an 

 important factor in cheapening our cleansing processes, a pure 

 rain water being the best attainable, whilst surface and river 

 water are .is a rule softer than spring water. 



I have now discussed the chemistry of cleaning as fully as 

 the time at my disposal will permit, and I hope the facts I 

 have brought before you will have quickened your interest in 

 soap, soda, and water, and will have helped to impress upon you 

 that without proper processes of cleansing, the health of each 

 unit, and therefore the prosperity of the masses, must suffer 

 deterioration. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



The following pass list for the degree of Doctor of Science 

 of London University has been issued ; — Experimental I'hysict : \ 

 Mr. Edwin Henry Barton. Chemistr)' : Mr. Bevan Lean, Mr 

 Thomas Kirke Rose, Mr. Arthur Landauer Stern, liol.any 

 Miss .Margaret Jane Benson. Zoology : Mr. .\rthur Willcy. 



IlKk MAjESrv's Commissioners for the Exhibition ol 1851 Iw^ 

 made the lollowing appointments to science research schol.u 

 ships for the year 1894, on the recommendation ofthcauth" 

 rities ol the respective Universities and Colleges. The scholar 

 ships are of the value of /^I50 a year, and are tenable for two 

 years (subject to a satisfactory report at the end of the first 1 

 year) in any University .at home or abroad, or in some other 

 institution approved of by the Commissioners. The scholars 

 are to devote themselves exclusively to study and research in 

 some branch of science, the extension of which is important 1 

 the industries of the country :— Scholar nominated by the Ur. 

 versily of Edinburgh, John Carruthers beattic; by the Univci 



