122 



SIR H. DAVY S AGRICULTURAL CHEMISTRY. 



tatioii of bread, wine, beer, and cider,* 

 The most essential requisites in every 

 process of fermentation, are, 



1. That the substance be in a fluid 

 state. 



2. That there be a proper degree of 

 warmth, that is, in general between 70° 

 and 80° of Fahrenheit's thermometer; 

 and 



3. That the atmosphere be not entirely 

 excluded from the fermenting bodies, nor 

 that they be exposed to a current of air. 



Filtration in chemistry as well as 

 domestic economy, is the process of 

 straining or filtering liquors, by means 

 of woolen, cotton, or linen, paper, or 

 other materials. The common filters 

 are of two kinds, namely: simple pie- 

 ces of paper or cloth, through which 

 the fluid is passed ; or similar mate- 

 rials are twisted up in the same manner 

 as skeins or wicks; they are first v^etted, 

 then squeezed, and one end put into the 

 vessel which contains the liquor to be 

 filtered; the other end is to be suspended 

 out of the vessel, lower than the surface 

 of the liquor, the purest parts of which 

 drop gradually out of the vessel, leaving 

 behind the coarser particles. Sometimes 

 they are made to operate while the liquor 

 is passing upwards in an inverted sy- 

 phon. 



SIR H. DAVY S AGRICULTURAL CHEMISTRY' 



(Continued from page 112.) 



5. Gluten may be obtained from 

 "wheaten flower by the following process : 

 The flower is to be made into a paste, 

 which is to be cautiously washed, by 

 kneading it under a small stream of water, 

 till the water has carried ofi" from it all 

 the starch ; what remains is gluten. It is 



*As the value of fermented liquids depend upon the 

 retention of the largest possible quantity of carbonic 

 acid. It is suggested for the consideration of brewers 

 and cider manufacturers, that in vessels containing 

 liquids, whilst undergoing vinous fermentation, the 

 vent for the escape of the gas shall be as small as pos- 

 sible, consistent with the safety of the vessel ; that the 

 gas be made to pass through a tube in form of a syphon, 

 and discharged under the surface of water, in such a 

 manner that atmospheric air shall not supply the place 

 of carbonic acid gas in the vessel, and that in the pas- 

 sage of the gas the largest possible quantity shall be 

 retained in water for domestic purposes, so as to par- 

 take of the properties of spring water. 



a tenacious, ductile, elastic substance. It 

 has no taste. By exposure to air it be- 

 comes of a brown color. It is very 

 slightly soluble in cold water, but not so- 

 luble in alcohol. When a solution of it 

 in water, is heated, the gluten separates in 

 the form of yellow flakes ; in this respect 

 it agrees with albumen, but difiers from it 

 in being infinitely less soluble in water. 

 The solution oi albumen does not coagu- 

 late when it contains much less than 1000 

 parts of albumen, but it appears that gluten 

 requires more than 1000 parts of cold 

 water for its solution. 



Gluten, when burnt, affords similar pro- 

 ducts to albumen, and probably differs 

 very little from it in composition. Gluten 

 is found in a great number of plants; 

 Proust discovered it in acorns, chesnuts, 

 horse chesnuts, apples, and quinces ; bar- 

 ley, rye, peas, and beans ; likewise in the 

 leaves of rue, cabbage, cresses, hemlock, 

 borage, safiVon, in the berries of the elder, 

 and in the grape. Gluten appears to be 

 one of the most nutritive of the vegeta- 

 ble substances ; and wheat seems to owe 

 its superiority to other grain, from the 

 circumstance of its containing it in larger 

 quantities. 



6. Gum Elastic or Caoutchouc, is pro- 

 cured from the juice of a tree, which 

 grows in the Brazils, called Haeva. When 

 the tree is punctured, a milky juice ex- 

 udes from it, which gradually deposites a 

 solid substance, and this is gum elastic. 



Gum elastic is pliable and soft, like 

 leather, and becomes softer when heated. 

 In its pure state, it is white ; its specific 

 gravity is 9335. It is combustible,and 

 burns wdth a white flame, throwing off a 

 dense smoke, with a very disagreeable 

 smell. It is insoluble in water and in al- 

 cohol; it is soluble in ether, volatile oils, 

 and in petroleum ; and may be procured 

 from ether in an unadultered state, by 

 evaporating its solution in that liquid. 

 Gum elastic seems to exist in a great 

 variety of plants ; amongst them are, 

 Jatropha elastica, Ficus indica, Jirto- 

 ccirpus integrifolia, and Urceola elas- 

 tica. 



Bird lime, a substance which may be 

 procured from the holly, is very analo- 

 gous to gum elastic in its properties. Spe- 

 cies of gum elastic may be obtained from 



