ALCOHOLIC FERMENTATION. 173 



" laughing gas "), and subsequently much the same kind of intoxi- 

 cation as alcohol, but not so long in duration. A remarkable 

 degree of insensibility to pain generally accompanies this latter stage, 

 whence the use of laughing gas as an " anaesthetic " (producer of 

 insensibility to pain) for dental and other surgical purposes. On 

 account of the danger of fatal results, should too much of the gas 

 be inhaled by persons suffering from weak heart and other 

 complaints, anaesthetics (laughing gas, vapour of chloroform, or 

 ether, &c.) should never be breathed except under medical direction, 

 or in the presence of some one acquainted with the proper methods 

 of use and precautions against danger requisite in the employment 

 of such materials. Dentists generally keep the gas stored in 

 strong iron bottles, into which it is pumped under great pressure 

 (fig. 77), and employ a specially constructed piece of apparatus for 

 the purpose of enabling the gas to be safely inhaled. 



Expt. 189. Decomposition of Sugar into Carbon Dioxide and 

 Alcohol. Several varieties of sugar are known to chemists ; thus 

 the ordinary table sugar is derived mostly from the beetroot or 

 sugar-cane, and is generally distinguished as cane sugar ; grape 

 juice and many other kinds of fruits (also honey) contain a 

 different sugar, known as grape sugar; cows' milk contains another 

 variety much less sweet to the taste, termed milk sugar (Expts. 89 

 and 120); and manna (an exudation from a species of ash tree) 

 contains a still different variety, called mannite. All these and 

 several other kinds known are capable of crystallising ; but besides 

 these, uncrystallisable varieties of sugar exist in treacle, golden 

 syrup, molasses, and such like substances. 



Many of these sugars, but not all, possess the remarkable 

 property of undergoing fermentation under suitable conditions; 

 that is, if the seeds or germs of certain minute vegetable growths 

 are introduced into solutions containing these sugars, the vegetable 

 matter grows and increases, and in so doing causes the sugar to 

 become split up or decomposed into carbon dioxide and alcohol. 

 In ordinary brewing the fermentable saccharine matter is mostly 

 derived from malt, or barley which has begun to germinate and 

 sprout by damping and keeping in a warm place, and has then 

 been killed by heating to such an extent as to destroy the vitality 

 of the seed without otherwise decomposing it ; if the heat be high, 

 the sugar present in the sprouting grain becomes more or less 

 browned or " burnt " (like the caramel or browned sugar used by 

 cooks for browning gravy, &c., made by heating sugar in a hot 

 oven), and gives a dark-coloured liquor on " mashing " or treating 

 with water to dissolve soluble matters, suitable for making stout 

 and porter ; whilst the light-coloured malts made by not heating 



