appeals strongly to most of their buyers—usually erection contractors—who recognize that the greater the spreading power the smaller the quantity of paint required, and, consequently, the less the cost. The bridge owner, on the contrary, is not interested in having his contractor use paint of the greatest possible spreading capacity, because the greater the said capacity the thinner the coating—and the thinner the coating the sooner will it become disintegrated by moisture, gases, etc. Of course, one can go to the other extreme by laying on the coat too thick, in which case it will run on vertical surfaces and will be too slow in drying on horizontal ones. Ordinarily, single coats of dried paint vary in thickness between one five-hundredth and one one-thousandth of an inch; and to produce this the spreading capacity is from eight-hundred to sixteen-hundred square feet per American gallon of paint.* The inspector of painting on bridgework, acting solely in the interests of the owner, should endeavor to have all paint applied just as thickly as it can be used without flowing on vertical surfaces. It should be daubed on thick at first, then gradually worked out by careful brushing so that it will flow into all the pores of the metal.

Distinction should be drawn between covering capacity and spreading capacity of paints. The former refers to the hiding capacity of the coating in relation to the surface on which it is applied, and is measured by certain standard tests on white surfaces, while the spreading capacity refers to the number of square feet of surface that can be covered by an American gallon of the paint.

Cement Paints

Portland cement as a pigment in bridge paints has begun to come into vogue of late years, the principal manufacturers of it being the well-known firm of Toch Brothers, and their product being designated "Tockolith." The author has not yet tried this brand of paint on any of his bridges, hence cannot speak from personal experience concerning its efficacy; but the fact that such a prominent bridge engineer as Dr. Gustav Lindenthal has used it on some of his largest structures is a guarantee that it is a first-class protective agent. However, Dr. Lindenthal is not willing to go so far as to state that Tockolith is superior to red-lead paints of best quality;  for  the  author  asked  him  the  direct  question  and  he  would  not  reply  affirmatively.  Toch Brothers have issued a very interesting little pamphlet "R.I.W. Steel  Preservative  Paints" (R.I.W.  meaning  "Remember  It's  Waterproof");  and  the reader  is  referred  to  that  publication  for  further  infor-

* Dr. Sabin prefers to adopt an area of 700 square feet per gallon of paint for red lead coatings, and states that graphite paints are supposed to cover from 350 to 600 square feet per gallon. He claims that red lead makes a stronger and more impervious film than anything else, hence can be safely put on thinner, and that three red lead coats, covering 700 square feet per gallon, make a final film seven one-thousandths of an inch thick.