OFFICE OF PUBLIC ROADS. 789 



It is expected in the following year to continue the study of this class 

 of road material with the view of determining accurately the water- 

 soluble portion, which will demonstrate the relative value of these 

 slags from a road-making standpoint. 



The adtlition of quicklime to basic blast-furnace slag screenings 

 has proved effective in the field experiments in increasing the 

 cementing properties and consequently the value of this class of road 

 bhiders. 



The investigations of Portland-cement clinkers have been under- 

 taken in connection with the study of basic open-hearth slag to 

 throw light, if possible, on the hydraidic properties of the latter 

 material. Samples of clinkers from the more important cement 

 mills have been examined microscopically, and the effect of water 

 upon them has been carefully recorded. This work will be continued 

 in the following year in conjunction with the slag investigations. 



CORROSION OF IRON AND STEEL. 



In the last annual report of this Office the results obtained in the 

 research work that has been carried on for a number of years on 

 the corrosion of iron and steel were described. A great deal of 

 progress has been made along these lines recently. As an instance 

 of this may be noted the improvements that have been made in cor- 

 rugated-iron culverts for road building and general drainage purposes. 

 The investigations carried on in the OfRce have led to the prepara- 

 tion by manufacturers of very much purer metal than has previously 

 been obtainable for the manufacture of culverts and pipes. In fact, 

 following the recommendations of one of our representatives, a 

 number of manufacturers are now turning out metal in great quanti- 

 ties which is almost entirely pure iron at a very sliglitly advanced 

 cost over the ordinary steels. There is every reason to beheve 

 that these purer irons are going to be of great service, for, although 

 it is not possible to make an iron that is entirely rust-proof, the pure 

 irons do not rust as rapidly or form pitholes as quickly as in the 

 case of more impure metals. 



As everyone knows, there have been great complaints during the 

 last ten years in regard to the quality and rust-resistant power of 

 wire fencing. This Office has taken this matter up and made a 

 thorough study of it. The representative of the Office has obtained 

 the cooperation of some of the leading and most influential manu- 

 facturers in the country. Investigations showed that much of the 

 wire fencing was not only made of inferior material, but that the 

 galvanizing was put on very thin. Since the investigations have 

 been going on it is safe to say that a great improvement has been 

 made by some of the manufacturers, who now seem willing to do 

 everything they can to improve their products. One of the methods 

 that is now in use for determining the amount of zinc that is carried 

 by wire depends upon dip])ing samples into a strong solution of 

 copper sulphate. This action destroys the zinc that covers the iron 

 in a very short time, and, by measuring the time that it takes to 

 destroy the coating, it is possible to obtain an idea of how heavily 

 the wire is coated. Several years ago it was hardly possible to find 

 galvanized fence wire in the open market which would stand one 

 minute in this solution. At present a great deal of the wire that 



