FIFTH ANNUAL YEAR BOOK — PART VI. 585 



seven constituents in most of the analyses; so that a great amount of data 

 has been collected, of much chemical interest and practical value. As seen by 

 the farmer, vinegar making is a simple process; to the chemist, though less 

 intricate than many other chemical transformations, it is complex; while to 

 the biologist, the various steps in the change of sugar in the fresh apple 

 juice to the acetic acid of vinegar are manifestations of very complex life 

 activities of many species of organisms, divided into two great groups, 

 yeasts and bacteria, each group performing a specific function in the change- 

 There may also come into action, under certain unfavorable conditions, 

 other bacteria which hinder the useful transformations, or which destroy 

 the products desired and thus lower the quality of the vinegar. This inter- 

 play of living organisms, sometimes for good, sometimes for ill, has not 

 been studied in all its details, and has been considered, in this investiga- 

 tion, only as results were produced, the chemical transformations alone 

 being considered. 



In a general way these transformations are two: Sugar, the ordinary 

 cane sugar and other forms known as invert sugars (dextrose and levulose) , 

 in the sweet cider, is first changed into alcohol through the fermentation 

 action of one group of organisms; then the alcohol, by the action of a second 

 group of organisms is changed to acetic acid. 



Chemically considered, each molecule of sugar consists of six atoms of 

 carbon, twelve atoms of hydrogen and six atoms of oxygen. When this 

 molecule of sugar is acted upon by the proper ferments, it passes through a 

 series of chemical changes which may be said to result, finally, in splitting 

 it up into two molecules of alcohol, each containing two atoms of carbon, 

 six of hydrogen and one of oxygen, and two molecules of carbon dioxide 

 gas, each containiMg one atom of carbon and two of oxygen. This may be 

 expressed in the form of an equation: 



Sugar Alcohol Carbon Dioxide 



Cg Hi3 Og = 2 Cg Ho O + 2 C O2 



Theoretically, we should be able to get from one hundred parts of sugar 

 by weight, about fifty-one parts of alcohol and forty-nine parts of carbon 

 dioxide; but because of evaporation and certain minor chemical changes we 

 can get in practice only about forty-five to forty-seven parts of alcohol or 

 less . 



After the alcohol is formed, the organisms which act upon it begin the 

 transformation to acetic acid. In this process oxygen is taken from the air. 

 The result may be similarly represented by an equation: 



Alcohol Oxygen Acetic Acid. Water 



C, He O + Oo = C3 H4 Oo + Ho O 



Theoretically, again, we should obtain from one hundred parts of alco- 

 hol about one hundred and thirty parts of acetic acid, but we usually get 

 less than one hundred and twenty parts. So, starting with one hundred 

 parts of sugar in the apple juice, we may get under favorable conditions 

 from fifty to fifty-five parts of acetic acid; therefore to have vinegar with 4.5 

 per cent of acetic acid, we must have juice containing not less than 8.5 per 

 cent of sugar. 



This percentage, however, is found in practically all ripe, sound apples, 

 although in a record of about one hundred analyses of eighty varieties of 



