4. After washing, the skins should be thoroughly worked on the beam, especially on the grain.
5. A solution of C. T. Bate is now prepared in the proportion of from one-half pound to one pound of bate in 100 gallons of warm water (90° F.). In making the solution do not have the water over 140° F. Under no circumstances boil it.
6. If the hides or skins have been treated as above indicated, one pound of bate should be sufficient for 400 pounds wet hide, washed from the limes. The hides or skins are placed in the bating solution and worked for an hour. They are then allowed to rest in the solution with occasional stirring for some hours or over night.
7. The length of time that the bating should continue will depend upon the degree of softness and pliability required in the leather. For instance, for sole-leather fifteen minutes is sufficient; for satin leather thirty minutes; for glove-leathers four to six hours or even longer.
8. On removing the skins from the bating solution it is sometimes desirable, especially for the finer grades of leather, to wash them in warm water and again work them over the beam. They are then ready to be placed in the tanning liquors.
9. In preparing the bating solution for the second pack, draw down the old solution one-third and replace with fresh water; then add in solution just one-half the quantity of bate used at first, and so on with each succeeding pack.
10. When fresh white limes are used toward the end of the liming process, and a manure bate is deemed necessary to reduce the harshness of grain caused by the fresh lime, it is very beneficial to give the skins from the manure bate a drench of C. T. Bate, thereby arresting the bacterial action of the manure bate, preserving the grain, besides cleansing, bleaching and neutralising the skins preparatory to placing them in the tanning liquors.
11. Again, when it is considered desirable to use a manure bate, it is good practice to treat the skins as above indicated (down to item No. 7), and then place them in the manure bate. By this previous treatment the antiseptic action of the C. T. Bate tends to arrest the destructive bacterial action of the manure bate, thereby lessening the risk of damage to the grain. In all cases where the value of the leather is dependent on the quality and perfection of the grain, this is an important advantage to gain.”
All these coal tar “bates” are rather suitable to replace drenching than bating or puering, as their effect is mainly that of removing lime. From their antiseptic character they are very useful in stopping the effects of putrefaction, and preventing ferments being carried into the tanning liquors, and skins may safely be kept at least for some days in weak solutions, but any necessary fermentive puering or bating should usually be done before and not after their use.
A writer in the ‘Gerber,’ 1875, p. 279, recommends the use of dilute solution of sulphide of sodium as a bating agent. Possibly it removes lime as sulphydrate, and the writer named seems to have obtained good results with glove lamb-skins. In experiments made at the Yorkshire College, a solution of 4 grm. per litre used on 40 grm. of pelt was found to plump it considerably, but probably a much weaker solution might be sufficient and more satisfactory. Polysulphides, such as “liver of sulphur,” or the yellow solution obtained by boiling dilute sodium sulphide or sodium hydrate solution with excess of sulphur, have great power of “bringing down” the pelt, and seem well worthy of experiment as bating agents.