Om Materialprøvningens Udvikling i Norden
Og om Statsprøveanstaltens Virksomhed

 152 now the point of view taken by the Laboratory was more likely to be, that common bricks should go through the older test, the strap test yielding no guarantee for the material being able to resist frost. The result of the last experiments could, on the other hand, also be interpreted in the way that these strap- tests did not, on the whole, yield any guarantee for any material being able to resist frost, so that, perhaps, in the long run it would become apparent that materials acknowledged to be able to resist frost according to this lest, froze to pieces nevertheless in nature. Thus, this question again arose as it had over and over again during the foregoing experiments viz., where is the great difference between sand-lime-bricks and common bricks in consequence of which a plain common brick can be placed directly on the bot- tom of the freezing-case without being damaged, while as a rule the best sand-lime-bricks are damaged to a great extent. Certainly, it had been clear, that the internal structure of the two materials differed somewhat, sand-lime-bricks consisting chiefly of sand-grains cemented together by calcic-hydrosilicate or the like, so that the rather large cavities between the grains com- municate by comparatively narrow outlets, the bricks on the other hand of a material either quite porous i. e. furrowed by many canals or for the very sandy bricks of sand-grains cemented together by a porous mass, but one had not been able to explain the different action of the frost in sand-lime-bricks and common bricks. — The Laboratory being, however, confident of having gained a clear understanding of this problem, an account will be rendered below of the considerations made and of some experiments which seem to prove the correctness of these con- siderations. In a sand-lime-brick generally more than 90 per cent (by weight) of the whole brick will consist of sand-grains i. e. a ma- terial not at all porous In the intermediate spaces a material will occur the porosity of which is not throughly known, but is probably not very great, and the mass of which is at any rate exceedingly slight as compared to that of the sand, and there will also occur cavities presumably much fewer in number and at the same time considerably larger than the pores in a common brick, the capacity of absorbing water and specific gravity generally not differing very much in common bricks and sand-lime-bricks. In