TESTING OF BUILDING MATERIALS BY SAND BLAST APPARATUS. 45 
fronds are generally not over 24 to 3 inches long, excluding 
the fine stalk which varies in length according to situation. 
It discolours in a similar manner as H. polyanthos and 
Stains the paper likewise with an oily impression. The 
peculiar odour is however not so strong as with H. poly- 
anthos. Distinct differences may be observed in these two 
ferns, but the peculiar odour as well as the oily exudation 
common to both characterises them as mere varieties of 
the same species. 
‘“‘H. bivalve can also not be keep green for many months 
after preparation. It dries a peculiar delicate green with 
a faint milky hue and discolours to a pale brown in a few 
months. It does not develop any peculiar odour after being 
dried, and does not always stain the paper and generally 
only faintly when it does. The stain however looks oily.” 
THE TESTING or BUILDING MATERIALS on 
ABRASION By THE SAND BLAST APPARATUS. 
By H. BurcHARTZ, Mitarbeiter des Koniglichen Material- 
prifungsamtes ftir Gross Lichterfelde, (Germany). 
(Communicated by Prof. W. H. WARREN, m. Inst. c.B. ) 
(With Plate I.] 
[Read before the Royal Society of N. 8. Wales, July 4, 1906.) 
IT is very important to select for building purposes the best 
materials, more especially if they are used for paving roads 
and sidewalks, or for covering floors. In addition to the 
price, the durability of the material must receive due con- 
sideration, but it is not so easy to find out a method for 
testing the wearing qualities, or the resistance to abrasion 
of materials which will give satisfactory and reliable results 
