44 



INFRA-RED TRANSMISSION SPECTRA. 



examination the cleavage section was perfectly transparent and much 

 thinner than the previous one. Furthermore, the dispersion is greater, 

 so that as a whole this large band is resolved into three components with 

 maxima at 2.5, 2.7, and 3^,. Beyond this region there are no marked 

 bands, while beyond 12 ^ there is complete opacity. The curve shows 

 depressions at 5, 7, 7.7, 8.2, 9.7, and 10.8 ju, but as a whole the curve 

 is conspicuous for the complete absence of sharp absorption bands, 

 except at 2.7 p, and is similar to glass and the micas. 



PORTLAND CEMENT. 

 (t 0.17 mm. Fig. 30.) 



The specimen examined was ground thin from a piece made for 

 tensile-strength tests, and, in making it, was mixed with 21 per cent of 

 water. The chemical constitution of Portland cement is unknown. 

 According to Le Chatlier 1 the action of water causes the formation 



I a 3 4- 67 



FIG. 30. Portland cement. 



of a hydrous silicate (2(SiO 2 CaO)5H 2 O) and a hydrous aluminate 

 (Al 2 O 3 4CaO.i2H 2 O). 



From the present curve it will be noticed that the substance is very 

 opaque, with a large absorption band at 3 p, which would seem to indi- 

 cate hydroxyl groups. From the curve of mellite and alum it appears 

 that Portland cement is too transparent beyond 3 ^ to contain 17 mole- 

 cules of water of crystallization, as indicated in the aforesaid formula?. 



MANNITE (CoH(OH) e ). 

 = 0.05. Curve a, fig. 31.) 



This substance is a hexahydric alcohol. The film examined was a 

 semi-transparent (due to crystallization) solid, between rock-salt plates. 

 The transmission curve has the general characteristics of the alcohols, 



J Le Chatlier: Annales des Mines, Feb., 1888. 



