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the paste can be spread out without cracking on the suface.

Trowel the paste on the glass to thin edges, and set the pat thus made aside in a damp chamber, and observe the time that elapses until (1) it will bear the quarter pound standard needle without appreciable indentation; (2), the weight of the one pound standard needle without appreciable indentation.

Tests for Strength.- Mix up the mortar consisting of three parts standard crushed quartz stone and one part Portland cement, proportion being taken by weight. Mix the sand and cement thoroughly until the mixture presents a uniform color. Gauge with about eight per cent. of water and work over the mixture thoroughly about six times. Tamp in molds in layers, and finish the surface of the briquette. Record the initials on one corner of the briquettes, and leave the briquettes in the molds. They will be taken therefrom by the instructor and placed under water after twenty-four hours.

SECOND Day's WORK. At the laboratory period one week following, the briquettes are to be taken from the water and tested for strength.

Tests for Fineness of Grinding.–Sift about four ounces of cement through No. 100 and No. 80 sieve and weigh the residue left on the sieves.

The Report.- Each student should report the results of the tests made by him as an individual to determine the fineness of grinding, the time of setting, and the strength of the five briquettes. Reports should be made on blank forms provided for that purpose.

Special instructions are issued to civil engineers.

AN ELEMENTARY COURSE IN PROPERTIES OF

MATERIALS.

BY GEORGE L. CHRISTENSEN, Assistant Professor of Mechanical Engineering, Michigan College

of Mines.

Instruction in the properties of engineering materials should have the following objects in view:

1. To illustrate the behavior of materials under stress.

2. To establish clear and definite conceptions as to the meaning of such fundamental terms as elastic limit, yield point, ultimate strength, percentage of elongation, modulus of elasticity, resilience.

3. To familiarize the student as far as possible with the methods by which materials are tested to obtain numerical results indicating their qualities.

4. To fix in the memory a few of the average numerical values for the more common materials such as cast iron, wrought iron, steel, timber, stone and concrete; thus establishing a very convenient mental standard of reference for the more detailed study of these and kindred materials, and at the same time forming the basis for that ready judgment so essential to the engineer.

5. To illustrate the use of these numerical values in simple problems of designing, thus associating and connecting the material itself, and the mathematical considerations involved, and laying the foundation for that habit of thought which must ever recognize the material in its various strengths and elasticities, in every problem of design.

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a céze S 3 2018 of astrao ne serca vort The 16:48 2: gato Teee weeks, three sitats de ses es per week The terruis Jacoche sins of construe01" Toe ciass, ce stadens is divided in teree sertices of the ease for recitations, and art of teese section is szaa Ended into two laboratory disons of ten students eac, rating in all six la statory ditsions. During a portion of the course, tie first recitation period of each week is set aside for laioratory i..nstration Fort, wien, instead of the whole mention mcesieg in the class-room, one of the small laboratory disisions of ten students meets in the laboratory, the other division taking some other hour of the same day. With this organization of the class it is possible to undertake a series of tests, the whole class being maste familiar with the plan and scope, but each laboratory division doing only a small part of the work.

Beginning the course, the first week is devoted to a class-room consideration of definition of terms and the behavior of materials under tensile stress. In the laboratory period of the second week, tensile tests are made of two specimens both cut from the same wrought iron or mild steel bar, one being rough, one inch in diameter, and the other turned down to a smaller size (Fig. 1). The group of ten students gathers around the testing machine—there is room enough for all to note everything that takes place-and each student is

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No. 27

Petested Specimens

Fig. 1.

required to keep full records just as though he were making the test individually. This being the first test, the construction and operation of the testing machine is explained. The rough bar is tested first. It is marked off in the presence of the class, with punch marks an inch apart, and placed in the machine. As the test proceeds, attention is first directed to the detection of the yield point by noting the drop of the beam, then the breaking down action is watched as shown by the loosening of the mill scale, then interest centers in the rapid stretching of the bar, readily noted with a pair of dividers, and finally, in turn, the ultimate load, the

necking down action, and the breaking load are noted. The broken specimen is passed around, it is handled and examined. They note that it is warm. They see the form of fracture and compare it with that of specimens pictured in the text-book. The diameter of the broken section is measured, and, finally, the broken ends are placed together and the elongation in lengths of

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2, 3, 4, 5, 6, 7 and 8 inches is measured with a pair of dividers, always keeping the broken section as near the middle of the measured length as possible. The test of the other specimen is then run through rapidly, noting all the results the same as for the first. A neatly-written report of these tests with computed significant results, and a diagram (Fig. 2), showing the variation in percentage of elongation when based upon

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