Page 67 Advertisements Column 2

Progress, Volume IV, Issue 2, 1 December 1908, Page 67

Portland Cement. (To the Editor Progress.) Limestone Island, October 12, 1908. Sir, — I have read with much interest in your October issue an article by Mr. Longley on "Portland Cement." While I quite agree with most ot his statements, theie aie two to which I beg to take exception very strongly, as I believe them to be not in keeping with the best practice among Portland cement users, and one of which would be certain to cause your readers much trouble if accepted by them. The first is " . .' . it being of the utmost importance that the pieces of the various materials should be angular and not round." Admitting that a few authorities have expiessed the opinion that angular stone makes stronger concrete than rounded pebbles, it will be found that they do not attach much importance to the matter. And in practice I have never known a large contractor to pass over a good, clean gravel for a crushed stone of equal cost. My own experience has indicated that a clean gravel is usually the best material, being stronger than any aggregate but trap rock or granite, and I have just completed several foundations and pedestals for very heavy machinery in which some 25 tons of gravel were used. The house in which I live is built almost entirely of concrete made with local cement ("Crown" brand) and shingle in tthich it would be practically impossible to find a single angular stone But the statement to which I most strongly object is that cracks m concrete work are caused by "laying one coat on another before the lower one has propeily set." This is in direct contradiction to the generally accepted idea that a perfect bond can be obtained only by putting on the top coat before the under one has set, and should, if intended to be taken seriously, be accompanied by convincing proof. I will not say that letting the under coat set hard causes the top one to crack, but I have investigated case after case where the falling away of the top coat was due solely to having let the bottom layer set hard before applying the top one. Hoping that in the interests of concrete you will consider this of sufficient importance to put before your readers. — Yours, etc., D. M. GBEEK, 8.A., Ch.E., M.Am.Ch.Soc.

Roller and other Bearings. (By Geo. B. "Woodruff.) Paper read before the Institute of Marine Engineeers on Jan. 13, 1908. (Continued) Flexibility of roller ensures full line of contact as compared with series of points, with either solid roller or ball, consequently a uniform distribution of load is obtained, and no tendency to destroy the surface of a journal, entirely eliminating the necessity of hardened and giound steel sleeves, any reasonable steel surface being entirely satisfactory. Boilers act as oil reservoirs, and light and left spirals as oil carriers. Less co-efficient of friction, hence higher efficiency than any other design. Less cost of installation due to elimination of special surfaces. As will be seen from the previous discussion, the flexible roller bearing, from the very principle on which it is designed, has many points of superiority, and in order to prove my contention in the matter, I propose to refer to a number of tests, which have been made in the past by people whose authority cannot well be questioned. In order to obtain experimental information showing the difference between the flexible rollers and the ordinary solid rollers, a series of experiments were made under several conditions by the Franklyn Institute of Philadelphia, and the results of these experiments, which involved considerable time in the execution, are condensed in the following: — 1 Hyatt flexible rollers, and 4 solid steel rollers, all uniformly %in. diameter, and lOin. long, were used in the test. The Hyatt rollers were formed of strips of steel %in. wide and %in. thick. These rollers were placed between three plates as shown in the sketch. The whole was placed between the plates of a testing machine and vertical pressure applied. Whilst under this pressure in a testing maehme, a horizontal pull was applied to the middle plate, which we will call B, and the resistance to rolling accurately measured by