116. Conclusions

The purpose aimed at in the test for time of setting will, to a certain extent, regulate the method to be employed. The pressure of the finger nail will be sufficient to determine (after a little experience) whether a cement will answer a certain purpose in this regard. But, if one is working to rigid specifications, or pursuing investigations as to the effect of different treatment on time of setting, it becomes very desirable to have a method of determining and defining the consistency of the mortar, and an accurate method of determining the rate of setting.

In the author's experience, the Vicat consistency apparatus as modified by M. LeChatelier (see § 99) has proved unsatisfactory except for thin pastes of neat cement or mortars containing less than two parts of sand. If the paste is not of such a consistency as to run freely into the ring, or "vase," an error may be introduced in the method of filling the latter. In operating with a natural cement it was found that a neat paste, in which the water used was 32 per cent, of the dry cement, required a gross weight of 640 grams to make the disc (1cm. diameter) penetrate midway in the vase; with 33 per cent, water, a weight of 410 grams was required; 34 per cent., about 250 grams; 35 per cent., 175 grams; 37 per cent., 155 grams. It would seem that some modification of this apparatus might be made which would not only indicate when a thin, neat cement paste has the assumed "normal" consistency, but which would also define the consistency of a given mortar, whether of neat cement or of sand mixture.

General Gilmore's wires are very simple, and will perhaps answer the purpose of obtaining the time of setting as well as any method in use. They can be used somewhat more accurately if the wires are made to slide vertically in a frame, than when held in the hand.

The necessity of care in all of the details of this test, temperature and amount of water, amount of gaging, character of medium, etc., has been sufficiently emphasized in the preceding paragraphs.