POPULAR MISCELLANY. 



547 



time to time as occasion may require. Every 

 cistern intended to hold water for drinking 

 should have a filter. For this pur])ose a 

 chamber can be parted off on one side the 

 cistern, within which the suction-pipe takes 

 the water for use, and the filtering material 

 placed so as to pass the water through holes 

 in this partition. Sometimes soft or half- 

 burned bricks are used for this partition, 

 through the pores of which the water passes 

 freely, if suflScient surface be used. If, how- 

 ever, it be desired to remove any dissolved 

 impurities from the water, these mechanical 

 filters, whether brick, gravel, sand, or sponge, 

 are useless, and recourse must be had to a 

 charcoal or spongy iron filter, which acts 

 chemically upon various substances in solu- 

 tion, burning them up, as it were, by the 

 oxygen within the filter. 



These filters, however, require such fre- 

 quent cleansing for the renewal of their effi- 

 ciency, that they can only be used eff'ective- 

 ly in a portable form, and cannot therefore 

 be built into the tank. 



Prodnets of Coal -Gas Combustion. — 



From a lecture by Mr. Thomas Mills, before 

 the British Association of Gas Managers, we 

 take the following remarks on the products 

 of combustion of coal-gas : " Of such gas, 

 supposing its specific gravity to be '5, or 

 half that of air, a cubic foot contains about 

 half its own weight of carbon ; and, if this 

 cubic foot of gas be burned, it will give a 

 little more than half a cubic foot of carbonic 

 acid, or, in weight, 488 grains. Again, a 

 cubic foot of coal-gas, of "5 specific gravity, 

 contains about 41 grains of hydrogen, and 

 this hydrogen in burning will produce 372 

 grains of water. If we regard the quantity 

 of air necessary to supply the requisite 

 quantity of oxygen to a cubic foot of gas, 

 it lies between five and six feet of air. For 

 every cubic foot of gas burned we require 

 the oxygen of between five and six cubic 

 feet of air, and this will give half a cubic 

 foot of carbonic acid as a result. When 

 we come to estimate the total products of 

 gas-combustion in such a place as London, 

 the figures are really startling. The quan- 

 tity of gas consumed in London annually 

 may be taken approximately at about 15,- 

 000,000 cubic feet. The amount of car- 

 bonic acid given off during a year by the 



combustion of these 15,000,000 of cubic 

 feet is 433,000 tons. The amount of water 

 produced by the combustion of this quan- 

 tity of coal-gas is 360,000 tons, or 80,000,- 

 000 gallons. One of the largest, if not the 

 largest gasholder-tanks in Loudon, is at the 

 Phoenix Works at Kennington. That gas- 

 holder-tank, supposing it had no internal 

 cone, and were perfectly flat at the bottom, 

 would hold 10,000,000 gallons of water, if 

 filled to the brim. You might empty that 

 tank and fill it eight times over in a year 

 with the water produced by the burning 

 of the coal-gas consumed in the metropolis 

 during that time." 



How the Pengnin rears its Yonng. — In 



the southern part of the Indian Ocean — 

 about latitude 40° south, longitude 80° east, 

 or about half-way between Africa and Aus- 

 tralia — are the two islands, St. Paul and 

 Amsterdam, both of recent volcanic oi-igin, 

 and both the favorite resort of the albatross. 

 But they are most of all remarkable for the 

 number of penguins which have here their 

 permanent residence. According to a writ- 

 er in Chambers's Journal, these penguins 

 form a rude sort of commonwealth among 

 themselves. In the rearing of their young 

 they exhibit considerable dependence on 

 one another. The hens lay one or two 

 eggs, never more, in a hollow of the ground 

 or on a little grass. The task of incuba- 

 tion is performed by both parents, the one 

 " off duty " going to the sea to procure food 

 for itself, and when the young are hatched 

 bringing a supply for the family. " Where 

 tens of thousands of nests are collected to- 

 gether so closely that the visitor cannot 

 walk without demolishing new-born nest- 

 lings or eggs at almost every step, it is diffi- 

 cult to understand how each bird knows its 

 own nest, eggs, or nestling, as it appears to 

 be the case until the young are able to walk 

 about for themselves. Then the latter form 

 into 'infant school^,' presided over by sev- 

 eral matrons, and ask and receive food 

 from any charitable passer-by, and the so- 

 cial system, so far as it goes, has attained 

 its highest point. There is no longer any 

 recognition of menm and tuum, but a deter- 

 mination on the part of each adult to do 

 the best for the rising generation, without 

 regard to the petty rights of property so 



