VINEGAR 1081 



gravity 1-072 : this latter affords a vinegar containing about 5 per cent, of anhydrous 

 acetic acid. 



In every instance the fermentation must be carried to its utmost limit, or to zero at 

 least ; and in cooling the wort prior to fermentation, great care must be used to pre- 

 vent the accession of the acetous fermentation before the yeast is added; for if this 

 happens to any considerable extent, the nitrogenised matter of the yeast is then per- 

 manently retained in solution by the acetic acid, and this may give rise to the incon- 

 venience called the ' mother.' To secure a, perfect vinegar by Ham's process, as much 

 attention is required during the cooling and fermentation as for the finest ale ; and this 

 axiom cannot be too strongly inculcated into the minds of vinegar-makers. The heat 

 of the fermenting tun should not exceed 76 Fahr., as the alcohol formed by the process 

 is apt at a higher temperature to pass off in considerable quantity with the carbonic 

 acid, and thus give rise to a loss of vinegar. Presuming that the fermentation has been 

 well conducted, and that the specific gravity of the wash is as low as water, or 1 '000, 

 the next step is to pass it through that apparatus which constitutes the great peculiarity 

 of Ham's process. This process is called ' the acetifier.' Ure. 



Impurities and Adulterations. 



In order to prevent the putrefactive change which often takes place in vinegar, 

 when carelessly prepared by the fermentation of malt-wine, &c., it was at one time 

 supposed to be necessary to add a small quantity of sulphuric acid. This notion lias 

 long since been shown to be false ; nevertheless, since the addition of 1 part of sul- 

 phuric acid to 1,000 of vinegar was permitted by an Excise regulation, and thus the 

 practice has received legal sanction, it is still continued by many manufacturers. So 

 long as the quantity is retained within these limits, and if pure sulphuric acid be used 

 (great care being taken that there is no arsenic present in such oil of vitriol, as is not 

 unfrequently the case in inferior varieties), no danger can ensue from the habit; but 

 occasionally the quantity is much overpassed by dishonest dealers. 



Dr. Ure mentions having found by analysis in a sample of vinegar, made by one of 

 the most eminent London manufacturers, with which he supplied the public, no less 

 than 175 grains of the strongest oil of vitriol per gallon, added to vinegar containing 

 only 3 T 6 s ths per cent, of real acetic acid, giving it an apparent strength after all of only 

 4 per cent., whereas standard commercial vinegar is rated at 5 per cent. 



The method of determining sulphuric acid has already been given, under the head 

 of ACIDIMETKY, and the same remark applies to hydrochloric acid and others. 



Hydrochloric acid is rarely intentionally added to vinegar ; but it may accidentally 

 be present when the pyroligneous acid has been purified by Volckel's process. It is 

 detected by the precipitate which it gives with solution of nitrate of silver in the pre- 

 sence of nitric acid. 



Nitric acid is rarely found in vinegar. For its method of detection, see NITRIC 

 ACID. 



Wine vinegar generally contains tartaric acid and tartrates ; but it is purified from 

 them by distillation. 



Sulphurous acid is occasionally met with in pyroligneous acid. This is recognised 

 by its bleaching action on delicate vegetable colours, and by its conversion, under 

 the influence of nitric acid, into sulphuric acid, which is detected by chloride of 

 barium. 



Sulphuretted hydrogen is detected by acetate of lead giving a black colouration or 

 precipitate. 



Metallic Salts. If care be not taken in constructing the worm of the still of silver 

 or earthenware, distilled acetic acid is frequently contaminated with small quantities 

 of mebil from the still, copper, lead, tin, &c. These metals are detected by the addi- 

 tion of sulphuretted hydrogen, as is fully discussed under the head f the individual 

 metals. Copper is the most commonly found, and it may be detected in very minuto 

 quantities by the blue colour which the solution assumes on being supersaturated with 

 ammonia. 



It is not uncommon to add to pyroligneous acid, a little colouring-matter and acetic 

 ether, to give' it the colour and flavour of wine or malt vinegar ; but this can hardly 

 be called an adulteration. 



The presence of the products of acetifcation of cider may be detected by neutral- 

 ising the vinegar with ammonia, and then adding solution of acetate of lime. Tar- 

 trate of lime is, of course, precipitated from the wine vinegar, while the pearly 

 malic acid of the cider affords no precipitate with the lime, but may bo detected by 

 acetate of lead, by the pearly scales of malate of lead, hardly soluble in the cold. 



For a description of the manufacture of Wood-vinegar, see ACETIC ACID and PYHO- 

 LIGNEOVS ACID. 



