18 r,t l.LKTIX 1216, U. S. DEPARTMENT OF AGRICULTURE. 
material. Remove the covering and sample the exposed bed as for 
n local sample described above. 
Class II , -- Method of taking (lass II samples. — These are the most im- 
samples. portant samples, and should be taken by the engineer or competent 
inspector while work is in progress. 
(a) When t: e materials have been spread and intimately mixed 
in accordance With properly drawn clauses covering methods of 
construction, the engineer should fill a container at intervals of — 7 
feet, along the road, and also at such other points as his judg- 
ment may dictate, where evidence of unsatisfactory mixing is ap- 
parent. 
( b) Very prompt examination of these samples should be made 
in order that defects of composition may be remedied by the 
builder before consolidation has progressed. 
III. METHOD OF TEST. 
Analysis. 1:! Dry 500 grams of the material at a temperature of 2V1° F. 
(100° C.) to constant weight Gently pulverize to break down 
soft clods or masses, but not grind or break hard material. Pass 
through a 10-mesh sieve, weigh the material retained and record as 
"coarse material." Use the material passing the lo-mesh sieve as 
the starting point of a percentage analysis as follows: 
{<d Weigh out two samples of 50 grams of this material for 
duplicate analysis. Place each in a tared wide-mouth bottle 
(5 to (5 centimeters diameter and about 12 to 15 centimeters high.) 
(h) Mix with distilled water (about 200 cubic centimeters i and 
heat to simmering temperature for one hour. Allow subsidence for 
eight minutes and siphon to a depth of 8 centimeters from the 
surface of the liquid. (The depth of the liquid should be sufficient 
to leave about 4 centimeters below the point of siphoning.) Add 
distilled water and 5 cubic centimeters of diluted ammonia 
(1 :500), brush the material with a stiff brush, stir thoroughly. 
allow to settle for eight minutes, and siphon to a depth of eight 
centimeters from the surface. Continue this process until the 
supernatant liquid is clear. Be careful to wash the stopper and 
neck of the bottle free from coarse material before decanting. The 
washings may be drawn off, collected and evaporated to dryness 
for direct recovery of the fine sediment classed as "Total clay." 
Ordinarily the sediment loss or "total clay" is computed as a dif- 
ference. 
Note. — The "total clay" may be separated further by the centrifuge 
into "clay" and 'suspension clay" when desired. See methods used 
by the Bureau of Public Roads in its examination of subgrad* 
materials. 
14. Wash the contents of the bottle cleanly into a porcelain 
evaporating dish and carry to dryness on a water bath. The dried 
residue should be carefully scraped from the dish and passed 
through a nest of 20. 60, and 200 mesh sieves. The residue re- 
tained on each sieve is weighed and recorded as sand of the 
respective sizes. Their sum constitutes the total "sand." The 
residue passing the 200-mesh sieve and caught in the pan is 
weighed and recorded as "silt." Duplicate samples should check 
within 1 pel* cent. 
Character of (<') The course material should be examined for hardness and 
material. with the magnifying glass to identify its character as quartz, 
hard iron compounds, feldspar, schistose material, or indurated 
clay. Bard quartz gravels are valuable in themselves and as in- 
dicating the quality of the finer aggregate. Feldspar, mica, and 
clay nodules are worthless, and indicate that the accompanying 
soil is poor for road building. 
(6) The sands should be examined with the magnifying glass 
for identification, as quartz, and for the presence of mica scales 
7 Intervals of 500 feet are suggested. 
