DUST PREVENTION AND ROAD PRESERVATION, 1914, ye 
‘The following report covers the condition of the existing experi- 
ments on January 16, 1915: 
ExPrerIMENT No. 3 (PENETRATION MretnHop—Hort, Heavy Or). 
This experiment remains in fairly good condition, although it has 
worn to a somewhat rough and uneven cross section. No breaks have 
occurred, however, and only one worn depression was noted. 
ExrERmMENT No. 4 (PENETRATION MetHop—Cot1p, Lieur Oi). 
This experiment continues in fair condition, although it does not 
present as good an appearance as No. 3. A group of small worn 
places were noted just north of the middle of the section. 
EXPERIMENT No. 5 (PENETRATION MretHop—Hot, HEavy O11). 
This is decidedly the poorest of the remaining sections, and appar- 
ently demonstrates the lack of economy in reducing the wearing 
course of rock to less than 24 inches of uncompacted material. Sev- 
enteen worn depressions, ranging from one-half square foot to 2 square 
- feet in area were distributed throughout the section, and it was appar- 
ent that they had been brought to grade by filling with coralline rock. 
These will be patched with bituminous material and rock. : 
EXPERIMENT No. 6 (PENETRATION MetHop—Hot, Heavy Ott). 
This experiment continues in excellent condition after having been 
under rather heavy traffic for over 18 months, and is a successful 
demonstration of what can be accomplished in this form of construc- 
tion. The bitumen has flowed in a couple of places and is still lively, 
but the cross section is well preserved, and there is no evidence of ex- 
cessive wear. 
SUPPLEMENTARY REPORT OF EXPERIMENTS ON ROCKVILLE PIKE, 
MARYLAND, 1913. 
The original report of these experiments was given in U. S. Depart- 
ment of Agriculture Bulletin No. 105, and the following information 
covers their history to and including an inspection on February 9, 1915. 
EXPERIMENT No. 1 (REFINED Coat TaR—HotT APPLicATION). 
This experiment has shown somewhat marked fraying along the 
edges, and a very noticeable deterioration of a strip along one edge 
for about 400 feet where trees overhang the road. The underlying 
macadam is fast becoming exposed over fairly large areas, and at the 
time of inspection it appeared probable that the restoration of the mat 
will be necessary early in the spring of 1915. One single-track trolley 
