DESIGN OF TEST BAR APPLIANCES, ETC. 519
diameter of the one and one-eighth inch test bar, when this size bar is used, care must be taken in getting a good form to the t; whirl-gate." If that form shown in the cut at T, Fig. 122, is closely followed, it will be found to give an excellent whirl to the metal as it rises in the mould, so as to bring any dirt that may by chance flow with the metal into the mould up to the top of the casting, and thus cause all test bars to be of a sound fracture when broken. The '' whirl-gate *' portion of the pattern seen on the left of Fig. 122 is made of brass or babbitt metal. The fluidity strips UU are cast in the main patterns after they are finished to the proper size. These fluidity strips can be made of any thin piece of wrought iron or steel. To strengthen the union of the " whirl-gate " portion of the pattern with the body of the test bars, brass or copper wire is laid in the mould and " cast in." The size of the " whirl-gate " where it joins the one and one-eighth inch diameter bar is about one-eighth inch in thickness by one inch wide. For the one and five-eighths inch, one and fifteen-sixteenths inches diameter bars, make this part of the gate one and one-quarter inches and one and one-half inches wide respectively, maintaining the same thickness of one-eighth inch as above shown in the one and one-eighth inch diameter bar.
It will be noticed that iron-perforated bottom-plates are used instead of wooden "bottom boards to give a backing to the * ' cope '' and '' iiowel'' when up-ended in order to prevent the pressure of the metal from bursting the mould when cast at* such points. To secure these iron bottom plates in place rapidly, strips of iron are pivoted at F F, Fig. 124, on the main part ofstsld ask such, after having I''