RURAL EXGIXEEBIXG. 687 



(9) There is no apparent relatiou between the chemical composition of a 

 cement and the rapidity with which it reacts with sea water when brought into 

 intimate contact. 



(10) In the presence of sea water or simihir sulphate-chlorid solutions: (a) 

 The most soluble element of the cement is the lime. If the lime of the cement 

 is carbonated, it is practically insoluble, (b) The quantity of alumina, iron, oi- 

 silica present in the cement does not affect its solubility, (c) The magne.sia 

 present in the cement is practically inert, (d) The quantity of SOs present 

 in the cement up to 1.75 per cent does not affect Its solubility, but a variation 

 in the quantity present may affect its stability by affecting its rate of hardening. 



(.11) The change which takes place iu sea water when brought into intimate 

 contact with the cement is as follows: (a) The magnesia is precipitated, from 

 the sea water in direct proportion to the solubility of the lime of the cement, 

 (b) The sulphates are the most active constituents of the sea water and are 

 taken up by the cement. Their action is accelerated iu the presence of chlorids. 

 Mo definite sulphate compound was established, (c) The quantity of chlorin 

 and sodium taken up by the cement is so small that no statement can be made 

 as to the existence of any definite chlorid or sodium compound formed with the 

 cement. 



(12) The SOs added to a cement iu the ph'.ster to regulate the time of set is 

 chemically fixed >o that it will not go into solution when the cement is brought 

 into intimate contact with distilled water. 



(13) Metal reenforcoment is not subject to corrosion if en)bedded to a depth 

 of 2 in. or more from the surface of well-made concrete. 



Reports of road eng-ineers, J. H. Pratt et al. {N. C. GeoJ. and Scon. Survey, 

 Bien. Rpt. State GeoL, J911-12, pp. 21-56) .—This report Illustrates the work 

 that is being done by the road engineers of the State in giving special engineer- 

 ing assistance in the construction, maintenance, and repair of roads, culverts, 

 and bridges to certain of the counties and townships, particularly noting 

 cooperative work with the Office of Public Roads of this Department. 



Tar spraying and tar macadam in situ, T. Aitken {Surveyor, ^3 (1913). 

 2ios. 1118, pp'. 052, 958, 954, fig. 1; 1119, 978-980).— The author relates the re- 

 sults of extended sei*vice experiments in the use of high-pressure tar spraying 

 machines in surface treatment of macadamized roads and in making tar 

 macadam in place. 



Data from the maintenance and repair of several tar macadam roads by use 

 of hand and gravity sprayers and high-pressure sprayers show an economy of 

 as high as 9.25 per cent in some cases in favor of the high-pressure sprayer, and 

 also that its use is an effective remedy against dust formation and lessens 

 excessive internal wear. 



The necessary operations are described for using high-pressure tar sprayers 

 for making tar macadam in place. Tests of various binders with varying 

 volumes of traffic indicate the existence of many inferior brands unsuited to 

 the density of traffic, and indicate the advisability of adopting, by service tests, 

 binders of varying degrees of quality to suit different classes of traffic and 

 climatic and atmospheric conditions. 



The " sticky " test for bitumens, C. B. Osborne (Good Roads, n. ser., 5 

 (1913), No. 23, pp. 337, 338, flf/. 1).—A machine is described which has been de- 

 signed by the California Highway Commission to measure the adhesive or bind- 

 ing property of road oil. The machine shows the stickiness or binding power of 

 a thin film of oil between 2 cylinders, one of the cylinders being secured and 

 the other being revolved by means of the pull of a given load, the thin film of 

 oil acting as the resisting force to prevent this movement. The measurement 

 18440°— 13 7 



