174 



SCIENCE. 



[Vol. XIV. No. 345 



ises justify the more elaborate consideration recently given it by 

 Professor Hilgard of the University of CaUfornia. 



When, as is most commonly the case, this hardness is due to 

 the presence of large proportions of the carbonates of lime and 

 magnesia, it can be recognized by the extent to which the water 

 becomes turbid, or forms whitish scum or incrustations, when 

 boiled. Boiling, then, is one of the means for softening waters 

 that are hard and "curdle the soap" from this cause; and this 

 fact is well known to housekeepers, but owing to the inconvenience 

 of the application of this remedy, it is rarely resorted to except for 

 drinking-water. For this purpose boiling has the special and ad- 

 ditional advantage of insuring the destruction of any minute germs 

 of disease that might contaminate the water. 



To soften water for washing, a common and very good remedy 

 is the use of carbonate of soda (sal soda) in sufficient quantity to 

 bring down the lime and magnesia, and thus insure the proper so- 

 lution of the soap to form suds. Only there is too often a mistake 

 made in not allowing time for the soda to bring down the lime and 

 magnesia in a powdery form, which requires from half an hour to 

 an hour when the water is cold, but occurs very quickly when 

 the water is hot. When, as is commonly done, the soap is put into 

 the water while the lime is still in the gelatinous form and diffused 

 in the water, a certain amount of " curdling " will still happen, 

 and the washed clothes (especially flannels) will have that soggy 

 and unpleasant touch which is caused by the accumulation of the 

 lime and magnesia soaps in them. 



That it is undesirable to use soda for softening water to be used 

 for drinking hardly needs more than mention. The natural hard 

 waters usually contain quite as much of saline matters as is desir- 

 able in drinking water. Soda, however, does not in any manner 

 correct the sanitary condition of a water ; on the contrary, it aids in 

 keeping vegetable and animal matters in solution, and unless added 

 in very large excess does not interfere with the vitality of fungous 

 or other germs. 



By far the most convenient and effective mode of purifying 

 larger quantities of hard water for domestic use, is the introduction 

 of a definite amount of quicklime, proportioned to the requirements 

 of each particular water; a point that can be readily ascertained 

 by any one having an ordinary capacity for observation. 



The principle upon which this apparently paradoxical process is 

 based is this : The lime and magnesia in most hard waters are con- 

 tained in the form of carbonates, dissolved in the water by the aid 

 of free carbonic acid. Whatever drives off or takes possession of 

 this free acid will bring down the earthy substances in an insolu- 

 ble form, and thereon depends the efficacy of boiling as well as of 

 the addition of washing soda ; cooking soda or bicarbonate will 

 not produce the effect. Now, lime in the caustic condition, as 

 lime-water, or milk-of-lime, freshly prepared, will most effectually 

 take possession of any free carbonic acid, and will form with it the 

 same insoluble compound that, when hard water is boiled, settles 

 to the bottom or incrusts the boiler. Hence, when an amount of 

 clear lime-water, just sufficient to absorb all the carbonic acid in a 

 water, is added to it, both the lime added and the lime and mag- 

 nesia originally contained, are brought down in the insoluble form, 

 and the mineral contents of the water are diminished very materi- 

 ally, sometimes to less than one-half of the original amount. With 

 the sediments thus brought down there also usually comes a large 

 proportion of the vegetable or animal matters contained in the 

 water; so that instead of perhaps becoming putrid in a tank serv- 

 ing for domestic supply, water so treated will remain clear and 

 odorless for a long time if protected from recontamination by in- 

 sects, falling leaves, dust, etc. 



The only practical difficulty in carrying out this purification is 

 the ascertainment of the proper proportion of lime or lime-water to 

 be used, so that the water shall neither retain too much of its orig- 

 inal hardness nor acquire an unpleasant taste and astringent action 

 from an excess of lime. This can, however, be done quite readily 

 by a few tests with different proportions of lime-water, and the 

 very simple trial as to which will produce the least "curdling" of 

 soap when ready-made soapsuds are added in small proportion. 

 Whatever proportion of lime-water or lime satisfies this easily as- 

 certained condition, is the best for all purposes. 



Numerous experiments prove that for the waters of the wells. 



springs, and smaller streams, as well as the catchment reservoirs 

 of the middle coast ranges and their valleys, the best effect is usu- 

 ally produced by the addition of from one-tenth to one-twentieth of 

 clear lime-water. 



As one part by weight of pure, unslaked lime requires seven hun- 

 dred parts of water for its solution, a simple calculation shows that 

 the above proportion corresponds to from five to eight grains of 

 lime per gallon, or about three-quarters to one pound per thousand 

 gallons. 



In the practical working of this process it is best to have, for 

 small tanks up to one or two hundred gallons, a supply barrel in 

 which clear lime-water of full strength can always be kept on hand 

 ready for use. A few pounds of lime, slaked into a creamy mass, 

 may be put in the barrel, the sediment being stirred up from time 

 to time as the clear water standing over it is replaced. Of course, 

 in order to preserve the proper proportion, once determined, only 

 clear water must be used, otherwise more lime than is called for, 

 will be introduced into the water. The lime-water barrel should 

 be kept closely covered. 



For larger tanks it will be more convenient either to take a 

 weighed amount of unslaked lime for each one thousand gallons, 

 slack it into milk-of-lime and stir it in, or else to prepare a large 

 quantity of milk-of-lime which, when thoroughly stirred, will for 

 each measure (bucketful) contain a known amount of lime. This 

 would be the best way to handle cases in which the feeding water 

 of boilers requires to be corrected. It should, in this connection, be 

 understood that the lime treatment is very efficacious against the 

 frothing produced in boilers by waters containing a large amount 

 of vegetable matter, as is commonly the case in that from ponds 

 or other catchment reservoirs. 



The sediment that accumulates in tanks used for this treatment 

 is usually of a sandy nature, and not readily stirred up; it therefore 

 causes little inconvenience, and can be removed at leisure, from 

 time to time, as it becomes too large. 



It is true that, like some other household measures conducive to 

 sanitation and comfort, the maintenance of this system requires 

 some regular personal interest and attendance on the part of some 

 member of the family. If carelessly handled, there may be unac- 

 countable variations in the gastric conditions of the family, from 

 one extreme to the other, and the soap may curdle from the water's 

 natural hardness one week, and from excess of lime the next. 

 But there is no excuse for such occurrences, except as the result of 

 carelessness or negligence, and the advantage gained, whether as 

 to health or comfort, amply repays the trouble when these hard 

 waters require to be used. 



A NOVEL ELECTRIC BATTERY. 



A NOVEL and simple form of electric battery has recently been 

 invented in Italy. As described in the Rivista Technica, it con- 

 sists of conical vessels of cast iron and porous earthenware, with 

 nitric and sulphuric acid. An iron cone is placed point downwards 

 in a stand, and is partly filled with strong nitric acid. Into this 

 there is placed a cone of porous earthenv^fare containing dilute sul- 

 phuric acid. Then follows an iron cone surmounted by an earth- 

 enware one, and so on in a series, each vessel containing its respec- 

 tive acid. It follows that the inner surface of each iron vessel is 

 bathed in nitric acid, and becomes passive, acting the part of the 

 platinum or carbon in' an ordinary cell. The outer surface is at- 

 tacked by the dilute sulphuric acid, and takes the place of the zinc. 

 There are no connections to make, the simple building of the pile 

 putting all the parts into union. The earthenware cones are eight 

 inches in diameter and four inches in height, and contain five hun- 

 dred and fifty cubic centimetres of ten per cent sulphuric acid so- 

 lution. The iron vessel contains one hundred and ten cubic centi- 

 metres of nitric and sulphuric acids, the latter being three times 

 the volume of the former. Sixty elements, arranged in two piles, 

 have a resistance of ten and one-half ohms, an electromotive force 

 on open circuit of eighty-one volts, and on closed circuit of forty- 

 five volts, with a current of four and four-tenths amperes. After 

 five hours the difference of potential falls to twenty-eight volts and 

 the current to two and seven-tenths amperes. 



