TESTING OF BUILDING MATERIALS BY SAND BLAST APPARATUS. 47 
grain producing the grinding acts independently of its 
bearer, and that each grain touches only once, is demon- 
strated by the test with the sand-blast. The effect of the 
sand-blast is well known by the examples offered by nature, 
and by the various uses of this medium in some industries. 
What can be effected by the grinding influence of the 
sand blown by the wind during centuries is shown, for 
instance, by the renowned pyramid of Ghizeh; and it can be 
seen frequently how the dust and sand particles, in a few 
years, wear out and round off the edges and outstanding 
parts of buildings. This slow action of the natural sand- 
blast is imitated in a much higher degree by the artificial 
sand-blast employed for making dim glass, and cleaning 
the surface scales of rolled iron. 
The sand blast apparatus used for industrial purposes 
has undergone some changes in order to use it for testing 
building materials. Such an apparatus in use for abrasion 
tests in the Royal Institute for testing materials at Gr. 
Lichterfelde (Germany), is shown in the annexed figure. 
The working of this apparatus and its effect may be shortly 
described as follows :—From the sand chamber n the sand 
falls through small tubes q on to the plate a and thence by 
smali openings into a slit where it is raised by the steam 
and blown upwards against the piece under test. The 
steam entering through the pipe is dried in the cylinder b. 
To shut off the steam from the apparatus a valve is inserted 
in the steam pipe (this valve is not shown on the drawing). 
Another valve is placed at e and must be closed for some 
minutes before using the apparatus in order to heat the 
sand, as otherwise it would become wet by condensation 
of the steam; r is a valve for shutting off the sand. The 
1 Gary—Versuche mit dem Sandstrahlgeblase. Mitteilungen aus dem 
Kgl. Materialpriifungsant, Gr. Lichterfelde, 1904, Heft 2, S. 103, ff. 
Verlag J. Springer, Berlin. 
