216 



COMMON THINGS, NO. Ill, 



PUTKEFACTION — PREVENTION, fec. 



It was stated in our first article that when certain animal and vegeta- 

 ble substances are exposed to heat and moisture, fermentation takes 

 place, and acetic acid or vinegar is generated. In substances which con- 

 tain nitrogen or azote a different fermentation ensues, called putrefaction, 

 some remarks upon which, with the means for its prevention, will form 

 the subject of the present article. 



The decomposition of azotised plants and of animal bodies, lakes 

 place spontaneously when exposed to heat, air, and moisture. During 

 this process the elementary substances which entered into the composition 

 of the bodies form various new and gaseous compounds. The oxygen, 

 hydrogen, nitrogen, carbon, phosphorus and sulphur, tbrm by their com- 

 binations water, ammonia or hartshorn, carburetted, phosphuretted, and 

 sulphuretted hydrogen. Most of these gases, and especially the latter 

 possess an intolerable odor, the result of their combination every one 

 knows who has enjoyed a close proximity to a carrion. After the evo- 

 lution of the gases there remains an earthy residuum consisting of de- 

 cayed mould with charcoal. 



As putrefaction cannot proceed except on certain conditions, by remo- 

 ving these, the progress of decay may be retarded, or wholly arrested. 



The first mode of prevention is by the chemical changes of the azo- 

 tized substances, resulting in the formation of new and more permanent 

 compounds. 



Albumen is that substance which both in animal and vegetable bodies 

 has the greatest tendency to putrefy, and upon it all the processes for 

 their prevention are designed to act. When albumen is dissolved in wa- 

 ter, a moderate heat is sufficient to render it putrid, but when coagulated 

 by heat, or otherwise, it becomes insoluble and much less liable to 

 change. In this state it may be dried, and thus rendered unsusceptible 

 of spontaneous decomposition. 



Albumen may be coagulated by heat as is exemplified in the boiling 

 of eggs, the white of which consists principally of this substance. Af- 

 ter this operation they may be kept for a long time. 



It may be coagulated by acids without being separated from its solu- 

 tions. Vinegar is commonly used in this way for the preservation of 

 meats and vegetables. 



It may be coagulated by tannin, which also unites with the gelatin 

 of animal bodies and forms indestructible compounds. Upon this fact 

 the art of tanning is founded. 



