230 



THE INDIA RUBBER WORLD 



[April 1, 1911. 



WEIGHING THINGS IN RUBBER FACTORIES. 



IT IS sometimes claimed that chemists have not made good in 

 rubber lore, and that rubber manufacture has remained to this 

 day, essentially a handicraft wherein mother-wit, intuition and per- 

 sistent empiricism are the things that count. It is very true that 

 formulae cannot be trusted implicitly, and that a certain indes- 

 cribable sympathy with the whims of a nervously organized raw 

 material is a much more valuable asset than a knowledge of the 

 atomic theory. Nevertheless, in every great rubber factory to- 

 day, a laboratory is as much a matter of course as a president or 

 a boiler-room, a chemist has undoubtedly helped these com- 

 panies in their competition with others who place their trust 

 wholly in things mechanical and in mother-wit. 



Eveo' manufacturer, however, should appreciate the really 

 great and useful discoveries made through theoretical chemistry, 

 even when aware of its limitations, especially in the rubber trade, 

 and at the same time insist upon the importance of clear-headed, 

 practical appreciation of the more homely rule of thumb prac- 

 tice, where it is successful. 



The success of chemistry has been due, more than all else, to 

 the use of accurate weights and measures and keeping careful, 



.\n.\lvtic.\l B.\l.\nce. 



written records. Too much detail will distract the attention 

 from the main issue, but taking notes during an experiment is a 

 real relief to the mind, and pays in the long run. 



The question of weights is of the utmost importance. The use 

 of liquid measures has been very generally abandoned in favor 

 of weighing, as being more accurate. Balances are true, however, 

 only within a comparatively small range ; but by means of the 

 wonderful scries of weighing apparatus now on the market, it is 

 possible to weigh anything, from a steamship to a pencil mark. 

 Every rubber factory must necessarily have a number of balances, 

 covering a range of weights with a certain accuracy, but these 

 are too often used above or below their range of accuracy. If 

 the error were constant, beyond this range, it could be allowed 

 for. 



There are many tj'pes of balances for fine weighing. One, for 

 example, is so delicate that it indicates a difference in weight of 

 one-five hundredth of a milligram, or less than one-fourteen- 

 millionth of an ounce. For such balances there is furnished a 

 unit-weight, weighing 29.1666 grams; so that in quantitative 

 analysis, on the basis of this unit, each milligram represents one 

 troy ounce per avoirdupois short ton. The bearings in these bal- 

 ances are agate planes, resting upon agate knife-edges. 



There is also the multiplying scale, for use in counting small 

 articles of the same kind. This has a capacity of four pounds, 

 and is sensitive to one-two-hundredth of an ounce. They are 



usually made to count by tens or dozens, though larger multiples 

 could be supplied to order. In using, a dozen of the articles, laid 

 on the long arm, will just balance a gross of the articles on the 

 short beam. 



Rubber chemists have always been accustomed to test the spe- 

 cific gravity of rubber samples. For this purpose there are spe- 



MANUFACTiniERS' ESTIMATOR. 



cial hydrostatic scales, for weighing in water. There is a sample 

 balance of this type, and also a combination balance, which can 

 be used for ordinary weighing, as well as weighing in water. 

 This combination is an all around useful balance, having a ca- 

 pacity of one kilo, and sensitive to one-half centigram. Some of 

 the finer balances, sensitive to one-twentieth milligram, have also 

 an apparatus for taking specific gravity. 



For weighing cloth, or sheeted material of uniform thickness, 

 there are balances provided with a cutter to take out a small 

 unit square, so that the indicator gives the weight of a square 

 yard without the necessity of calculation. 



There is a type of balance called an estimator, very convenient 

 for rubber compounding. When a small amount of compound 



Counting ScALii. 



is weighed, the indicator will show, at the same time, exactly 

 how much of the material will be needed to make a batch of 

 rubber for any desired weight or number of similar articles, and 

 this with greater accuracy than can usually be done by figuring. 



When balances are occasionally moved, it is best to have them 

 fitted with screw feet and a spirit level, so that they can be trued 

 up for any table or counter. The hangings are of aluminum, for 

 lightness, and the metal parts should be of platinum, brass, or 

 otherwise made non-corrosive. It is best to have the whole en- 

 closed in a glass case, to exclude dust, and to keep the metal 

 parts at an even temperature. Very fine readings must be done 

 with a magnifying glass. 



Usually a set of weights goes with each balance, but these can 

 always be found in the general market, too, ranging from a 

 milligram (about one twenty-eight-thousandth of an ounce) to 

 50 pounds. The metal of these must be non-corrosive, since cor- 

 rosion increases their weight and destroys their accuracy. 



