PREFACE. xxv 



It will be noticed that comparatively few chemical analyses 

 have been made, most of those published being copied from 

 earlier reports. On the other hand, several hundred physical 

 tests were made, that is, tests O'f the air shrinkage, fire shrinkage, 

 color in burning, temperature of vitrification, and of fusion, etc. 

 It was believed that these tests would better supply the informa- 

 tion needed by the practical clay worker, particularly since an 

 ultimate chemical analysis may not be a true index of the char- 

 acter of the clay. In other words, two clays of nearly the same 

 chemical composition may behave quite differently in working, 

 "owing to the different ways in which the chemical elements may 

 be combined. 



As already indicated, the endeavor was made to obtain informa- 

 tion regarding the location and character of undeveloped clay 

 deposits. That we have succeeded in locating' all the unworked 

 clay deposits of the State, particularly in the sandy pines district, 

 is, of course, improbable. It is likewise certain that all the out- 

 crops of the clay deposits, which occur in regularly defined belts, 

 like the Raritan clays, the Clay Marl clays, I and II, and the 

 Alloway clay, have not been seen, but the zones within which 

 these may be looked for have been accurately determined and 

 shown upon Plates X — XIII, and many localities have been 

 sampled. Private endeavor must do the rest. Certain it is that 

 very few, if any, reports have ever been issued which give so 

 much detailed information regarding unworked and heretofore 

 unknown deposits. 



Two other special features of the report may be emphasized. 



The first of these is the series of tests on the breaking and 

 crushing strength of New Jersey brick and the deductions which 

 may be drawn from them (Chap. XI). So far as known they 

 are the most complete tests along these lines ever published in 

 this country, and it is believed that these results will be accepted 

 as a standard by all engineers. Acknowledgment must be made 

 to Prof. I. H. Woolson, of Columbia University, for the pains- 

 taking care with which these experiments were made. 



The other important line of investigation is that relating to 

 the chemical composition of fire brick and its relation to' their 



