There are numerous forms of mixing vats, all working however, on the principle shown in Fig. 51. In this, the vat _A_ is provided with a central shaft _C_ carrying radial mixing blades _E_. This shaft is driven by bevel gears _D_, _F_. As the rotation of these blades would merely tend to create a rotary current of molasses and water, and not to mix them, some means should be used for impeding and breaking up this current. To that end the cover is provided with downwardly projecting rods _I_ which create counter currents, and thoroughly intermingle the two liquids. Another and even better form of mixer consists of a tank into the lower portion of which enters a perforated pipe of relatively large diameter. This is provided at the end with an air entrance and a steam injector. The injected steam draws in air and the steam and air are forced under pressure into the vat, thus diluting the contained molasses, agitating it and thoroughly aerating it. [Illustration: FIG. 51.--Mixing Vat.] The molasses as it comes from the sugar house may contain anywhere from 30 to 45 per cent of sugar, and this should be diluted with water to a concentration of 16 to 18 per cent of sugar. The density of the wash after "setting up" is 1.060. It is to be noted that though with improved apparatus a wash as concentrated at 12∞ or 15∞ Baume may be worked; yet where simple apparatus is used six degrees or eight degrees is better and much more favorable to rapid and complete fermentation. After setting up, one gallon of strong sulphuric acid and 10 lbs. of sulphate of ammonia are added for each 1000 gallons of wash. This neutralizes the alkaline carbonates in the beet juice which would otherwise retard fermentation, and it assists the yeast to invert the cane sugar as formerly described. The addition of ammonia is in order to give food to the yeast and obtain a vigorous fermentation. The yeast used for fermenting molasses is prepared either from malt or grain and is used as concentrated as possible, and in the proportion of about 2 per cent. The "pitching" temperature of a molasses wash varies with the concentration of the wash, being higher for strongly concentrated solutions than for weak ones. When the wash tests as high as 12∞ Baume, fermentation begins at about 77∞ F. and is raised during fermentation to 85∞ or 90∞ F. A temperature around 82∞ F. is best on the average as this is most conducive to the growth of yeast. Where the vats are large and the syrup considerably diluted the temperature rises very quickly and must be moderated by passing a current of cold water through a coil of pipe on the bottom of the vat.