Page:Popular Science Monthly Volume 81.djvu/183

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steam, when the amount of the latter in the chloroform extract which is insoluble in benzol is at least 7.5 per cent, and the asphalt, separated according to the method of Marcusson and Erckmann, contains 1.4-3.1 per cent, of oil with at the most 0.6 per cent, paraffin.

A bitumen would be called a petroleum residual pitch if it contains at most 1.7 per cent, of sulphur, even in the chloroform extract prepared as previously described and further 26-59 per cent, of oil in which the paraffin amounted to 3.3-16.6 per cent.

These conclusions of Holde are confirmed by my own data given in the paper to which I have referred, and are of the greater value on that account.

It appears, therefore, that a native solid asphalt is characterized by the fact that it contains sulphur, and the same thing is true, though in a lesser degree, of the softer bitumens from which it is derived.

Aside from the mere fact that sulphur is present in asphalt it is undoubtedly true that some of the most important physical characteristics of the material and those which distinguish it from the residual pitches are due to its presence, that is to say, the greater lack of susceptibility to change in consistency with change of temperature in the solid asphalts than is the case of the residual oils and pitches.

It is the presence of such a large amount of sulphur derivatives in Trinidad and Bermudez asphalt which makes them so desirable for use in highway construction, as compared with the residual pitches