SCIENTIFIC NEWS. 



[July 1st, li 



far as Dr. Richardson's experiments have gone, it can be 

 breathed by cold-blooded animals. 



A further very curious fact is that such " devitalised " 

 oxygen can be restored to its vital state by the electric 

 action given off from a set of brushes connected with the 

 positive pole of a frictional machine. 



There is here evidently much yet to be learnt. But we 

 may at any rate draw the practical conclusion that it is not 

 merely needful for the air which we breathe to contain about 

 twenty-one per cent, of oxygen. We see that such oxygen 

 must not have been recently inhaled by men or other 

 animals. We find ourselves on the way at least to attach 

 a definite meaning to the term " stuffiness." We can 

 understand why the air of the sea, the forests, and the 

 mountains, should be felt as more refreshing and invigorat- 

 ing than that of towns. Lastly, we comprehend how a 

 thunder-storm in common phraseology " clears the air." 



Does the vitality of oxygen, perhaps, depend on a trace of 

 ozone, too small to be detected by ordinary chemical methods, 

 destroyed by passages through the lungs and re-created by 

 electric action ? 



CHEMICAL FIRE EXTINGUISHERS. 



FOR some time past it has been a common practice in the 

 United States to use glass hand-grenades, the contents 

 of which are capable of extinguishing fires rapidly. Their 

 introduction in this country is comparatively recent, but they 

 are rapidly growing in favour, and are much to be recom- 

 mended. The grenade is usually a glass flask containing 

 about a pint of fluid, and several of these are hung up in 

 places easy of access in the house, hotel, or other building 

 to be protected. When a fire is detected, one or more of the 



Fig. 3. 



grenades are immediately thrown on it and broken, and the 

 rapidity with which the fire is extinguished is very remark- 

 able. What the liquid consists of is an open secret, but no 

 satisfactory explanation has yet been given of the reason 

 why it puts out flame so quickly. That it can do so is an 

 undeniable fact, as we can testify from personal observation. 

 The best grenade is that made by the Imperial Fire Ex- 

 tinguisher Co., and is shown in the accompanying illustra- 

 tions. Fig. I being an elevation, and Fig. 2 an enlarged 

 view of a special device which is in effect a self-acting relief 

 valve for the escape of any gas which may be formed within 

 the flask. The bulb (a) is pierced with a small hole at 

 the top ; the hollow stem (b) has a twist or curl, and in 

 this a drop of liquid settles and forms a water seal at once 

 sensitive and secure, and the straight part of the tube is 

 fitted in the neck of the flask. By using this safety vent 

 there is no need for the glass to be thick, so that the 

 grenade can easily be broken when brought in contact with 

 any hard substance at the critical time of fire. 



THE SALT INDUSTRY. 



THE magnitude of the infinitely little has so many 

 examples in nature that we cease from earliest child- 

 hood to marvel at the universal application of the law. 

 Chalk cliffs, coral reefs, and other instances, are the 

 favourite themes of juvenile wonder books; whilst our 

 earliest memories of poesy are often associated with " the 

 little drops of water, little grains of sand," adduced as 

 examples for the infant moralist. If we wished to push the 

 comparison further it might be stated that " these little drops 

 of water " collectively hold in solution an amount of salt that 

 would occupy 4,419,360 cubic miles of space ; for such is 

 the quantity supposed to be held in solution by the entire 

 ocean of the world. This is equal to fourteen and a half 

 times the bulk of all Europe above water. 



To think that each time we sprinkle a taste of salt on 

 our food we are helping to undermine a large tract of the 

 British Isles. is a sufficiently novel and surprising idea at the 

 first blush ; but such is undeniably the case. Within the 

 last few weeks paragraphs have appeared in the daily 

 papers with a heading " Subsidences in the Salt Districts," 

 or some such title. We purpose in the present notice 

 giving a few particulars of the way salt is procured, and 

 the effect its abstraction from the earth has in the matter of 

 these subsidences, basing our description on a visit recently 

 paid to the chief salt-producing district of England. Before 

 proceeding, however, to our more particular description, it 

 will be well if we give a few general particulars on the 

 subject. 



Common salt, or sodium chloride, is divided industrially 

 into two kinds, respectively bay salt or sea salt, and rock 

 salt or mineral salt. The way that these are obtained for 

 commercial purposes will be described later. That both 

 kinds have a common origin in the ocean there is little 

 doubt. The vast layers of rock salt, hundreds of feet below 

 the surface of the earth, occupy a site that has in remote 

 geological periods had the wide ocean rolling above it. The 

 stratification of the beds of rock salt, interposed between 

 layers of clay, marine shells, and various crystals that can 

 only be formed in water, all point to this conclusion. At one 

 time nearly all the salt used was obtained by the evaporation 

 of sea water, and in some countries of much sunshine the in- 

 dustry is still largely carried on. In our own country, how- 

 ever, we have too little sunshine and the atmosphere is too 

 humid to enable the more natural process to compete with the 

 artificial methods we are about to describe. In Portugal over 

 250,000 tons of salt are obtained in this way from five works. 

 Spain contributes 300,000 tons from the Bay of Cadiz, the 

 Balearic Isles, etc. Italy makes 165,000 tons a year, and in 

 France 250,000 to 300,000 tons are produced. The " Salz- 

 garten" of Austria supply 70,000 to 100,000 tons annually. 

 As compared with these figures, which are taken from the 

 article "Salt" in the Encyclopaedia Britannica, it may be 

 noted that the Northwich salt district alone produced in 1881 

 1,600,000 tons of white salt and 166,740 tons of rock salt. The 

 way in which the salt is obtained by natural evaporation is 

 simple in the extreme, as indeed are all salt-producing opera- 

 tions. A tract of land near the sea coast is levelled and 

 puddled, and this space is partitioned off by a chequer work 

 of banks, the divisions thus formed being more and more 

 shallow as they are placed further away from the portal 

 where the sea water enters. The water flows from one di- 

 vision to another, the evaporating process going on all the 

 time under the heat of the sun. At last the point is reached 

 when the water is insufficient to hold the salt in solution, 

 and it therefore appears in solid particles which are collected 

 and stowed in heaps. The bitter salts, such as magnesium 

 chloride, which exist in sea water along with sodium chlo- 



