mitted its employment in certain of the larger members of long fixed-spans, but barred it entirely from movable spans.

In the specifications of "Bridge Engineering," written in 1915, no high steel is permitted, excepting only a certain grade of metal termed "machinery steel," for which the limit of reduction of area is 35% and that of the elongation in two inches is 18%, both of which values are somewhat greater than those specified for high steel in "De Pontibus."

Mayarí steel is a natural alloy of nickel-chromium steel, containing from 1% to 1.5% of nickel and generally from 0.2% to 0.75% of chromium (although occasionally the proportion of this last element runs considerably greater), with sulphur below 0.04%, phosphorus below 0.03%, and manganese as desired. The ore comes from a deposit of some 25,000 acres at Mayarí in the province of Oriente on the Island of Cuba. On account of the large irregularities in the elastic limit of Mayarí steel, it is not deemed safe to count upon more than 50,000 lbs., but as the nickel and chromium which exist in the ore cost no more than the iron, the actual cost of manufactured bridge members really ought to be about the same as for carbon steel, unless it be that the content of these foreign elements has to be increased. It may be that Mayarí steel will prove to be the basis of the future ideal alloy of steel for long-span bridges; but it is more likely that the irregularity of composition of the smelted metal will render its employment for that purpose too objectionable.

Thus far there has been no systematic attempt to use for bridgework the "purified steel" manufactured by the electro-metallurgical process, the main objection to it being that up to the present time it has never been produced in large melts or on a grand scale, as would be necessary if it were employed in steel structures.

As for aluminum steel, it has never even been in the running, although advocated for bridgework by a few engineers who apparently were not properly posted concerning its properties.

At one time the author had the hope that vanadium steel might solve the problem of alloy steel for bridgework; but from all he can learn of late about that alloy it appears to fall short in several essential requirements.

Silicon steel in bridgework has been tried, and with satisfactory results. It is about as difficult to manufacture as other alloy steels, the elastic limit being forty-five thousand pounds per square inch. It has not been very much used as yet, but those who have tried it seem satisfied with the results. It ought not to be very expensive per pound, as the alloying material is not costly.

Of late the element molybdenum has been looming up as a possibility in the solution of the high-alloy, bridge-steel problem, but thus far no experiments with it have been made looking towards its use in bridge construction. The author nowadays is indulging in a "pipe-dream" about what he has dubbed "Nichromol" steel, a prospective alloy of nickel, chromium, and molybdenum, with an excess of manganese above the amount