52 



THK TESTING OF ROAD MATERIALS. 



II. RATIONAL ANALYSIS. 



Tn the study <>t clays for various purposes a rational analysis is often called for, 

 in spite of its great inaccuracy undoubtedly gives results which are of some practical 

 value. The method as given by Meade," which is convenient ami rapid, in used 

 with some slight modification in this laboratory. 



Heat l.L'5 grams of the finely ground wimple with 15 cc of concentrated sul- 

 phuric acid to near the boiling point of the acid and digest for five hours at this 

 temperature. Cool, dilute, and filter. Wash and ignite the residue to a constant 

 weight, called A. After weighing, brush the residue, which consists of silica, present 

 [i- -and and undecomposable silicates and silica from the decomposition of the sili- 

 cates of alumina, into an agate mortar, grind very finely, and weigh 0.5 gram of it 

 into a platinum dish containing 50 ccof boiling caustic potash solution (1.125 sp. gr. ). 

 Boil for five minutes, filter, wash first with hot water and then with water contain- 

 ing a little dilute hydrochloric acid, and then again with hot water, dry and ignite 

 to a constant weight. Call this weight B. Multiply A by 0.4 (to correct the 1.25 

 LM-ams of clav used to correspond to the 0.5 gram of the residue taken for treatment 

 with caustic potash solution) and subtract B from the product. Multiply the differ- 

 ence by 200 to obtain the per cent of silica combined with alumina in the clay. 

 This deducted from the total silica found by analysis gives the silica as sand and 

 undecomposable silicates. 



TABLE A. Results of laboratory tests. 



;The starred figures are the results obtained by the new method, see page 42.] 



" I'.xamination of Portland Cement. 

 b High cementing value for slag. 



Chem. Pub. Co., 1901. 



