28 



NEW YORK STATE MUSEUM 



middle of the upper thin layers of the slip clay. At the junction 

 of the yellow and blue clays there is usually found a layer of 

 concretions consisting mostly of calcium carbonate. 



The ordinary blue clays are usually very plastic and require 

 about 29 per cent water in order to place them in condition for 

 proper working when used in the manufacture of soft-mud brick. 

 The air shrinkage is about 6 per cent, and when burned at cone 1 

 (about ii50°C) there is no fire shrinkage. The burned product 

 is of a pink color and is usually comparatively soft. The brown 

 clays require about 26 per cent water for proper working and have 

 an air shrinkage of 7.5 per cent. Burned at ii5o°C there is a fire 

 shrinkage of 1.5 per cent, giving a very red, dense vitreous product. 



The slip clays are produced mainly in the vicinity of Albany. 

 No attempt has been made to open pits or banks on an extensive 

 scale, and no method of artificial drying is attempted by those en- 

 gaged in the slip clay trade exclusively. The clays are shoveled 

 from the banks, placed on racks to be dried by the heat of the 

 sun and then drawn to the railroad siding and loaded. 



Chemical analysis of the slip clays shows that there is consider- 

 able variation in the percentages of the ingredients but that the 

 alumina is usually low, considerably below that present in the 

 brick clays. The following analyses illustrate the composition of 

 the slip clays of the Hudson valley. 



SiO.3 



Al 2 Os.. .. 

 Fe a 8 . . . . 

 T1O2.... 

 CaO .... 

 MgO.... 

 KiO . . . . 

 Na»0 . . . 

 Moisture , 

 Ignition . 



Total, 



59-04 

 11.80 

 5-56 

 1 .00 

 7.81 

 3.00 

 2.29 



• 53 



• 93 



58 • 44 



15-65 



3-43 



.90 



7.02 



5.18 



2.28 



.29 



•75 



6 59 



76 

 .00 



•50 

 .10 

 . 12 

 .40 



■ 73 

 •49 

 ■64 

 .92 



100.53 



99 . 66 



00 [0 



59.68 



14. 16 



1.76 

 .90 



6.68 

 484 

 2.75 

 .40 

 65 

 7.75 



9957 



1 Slip clay from Albany, upper banded la\ its. 



3 Slip clay from Albany, upper banded layers. 

 ,i Slip clay from Albany, lower massive beds. 

 1 Slip clay from Albany , lower massive beds. 

 5 Slip cla; from Alban , a i pi i ba 



