Testing of t h e strength of glue jellies has been carried on in this laboratory for a great many years, and under t h e direct supervision of t h e writer for t h e last 2 1 years. I n t h a t time all kinds of devices have been used for this purpose, but until the Smith glue tester (Fig. I ) came out, there was none on t h e market sensitive enough t o show even fairly large differences or t o duplicate t h e "finger test" so valuable in the hands of an expert. This form of tester is far

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... ior t o any other we have seen, b u t in its original form the testing, although sensitive enough, was subject t o some errors which affected t h e grading of t h e glues. Moreover, since i t was filled simply with water colcred with a dye t o make i t visible on the scale, glues were often met with which could not be measured on t h e scale. The only modification of t h e Smith glue tester t h a t we have seen illustrated is t h a t of E . C Hulbertl (Fig. 3). E n FIG. 1 C FIG. 2 The apparatus used in this laboratory ( Fig. 2 ) consists of a Smith glue testing apparatus modified t o give more accurate results for grading glues correctly. Mercury is used in the U-tube, and above^ this colored water. The scale has slots a t each end t o allow of moving i t and setting it by the screws t h a t fit through t h e slots. All other parts of the instrument are as illustrated in Fig. I . It was first determined by calculation and experiment t h a t t h e use of mercury covered by water in t h e scale tube gave correct results. It was found necessary t o correct for the force required t o deform the diaphragm itself, for this takes some force t h a t should not be credited t o t h e jelly, and this force is not a constant, for diaphragms vary much with different rubbers and vary from day t o day through permanent stretch of the rubber. Another point is t h a t it is necessary to find the force required t o deform t h e rubber when t h e instrument is set in t h e position for a test, that is, when the water stands at point A in the diagrams. Owing to changes in temperature of t h e water and The principal modifications are the use of mercury covered by water in t h e scale tube, and the use of air, instead of water, in the thistle tube, the mouth of which is covered with a thin, dental rubber diaphragm, as in the original Smith glue tester. The use of mercury is a distinct improvement and has been followed in this laboratory for years. We do not readily see the advantage of t h e substitution of air for water in t h e thistle tube, especially since leaks are not so easily noticed in the rubber diaphragm or where it is attached io t h e thistle tube. T H I S JOURNAL, 6 (1913), 235. FIG. 3 mercury in the instrument or of the whole instrument, t h e water will not always stand at the zero mark of the scale, as i t should in starting a test. To overcome this trouble we made our scale movable in a vertical direction. With these modifications and methods of application we found we could properlygrade our glues or glue jellies very closely and with comparative correctness. WETHOD O F USE Our instrument is kept permanently in a chill room connected with t h e laboratory and maintained close t o 40' F., a t which temperature the glue jellies are.