938 



SCIENCE 



[N. S. Vol. XXV. No. 650 



their chemical equivalence; thus 40 MgO has 

 the same lowering effect as 56 CaO, or 62 

 Na^O. This is called the Law of Eichter, but 

 it does not apply to glazes where the amount 

 of fluxes is large. Eusibility of clay is de- 

 termined by test pieces (Seger cones), or by 

 pyrometry. The Seger cones are made of 

 pure clay, mised with fluxes in such graded 

 projKirtions that the fusion temperature of 

 the consecutive numbers are about 20° C. 

 apart. The No. I. cone fuses at the same 

 temperature as an alloy of one part platinum 

 and nine parts gold, i. e., at 1,150° 0. Since 

 this temperature is rather high, Cramer and 

 Hecht prepared cones containing B2O3 and 

 PbO, fusing at definite temperatures down 

 to 590° C. These cones give the true meas- 

 ure of the heat effect, but not necessarily 

 the exact temperature, and hence are more 

 useful to the potter than is the pyrometer, 

 since they show the effect which will be pro- 

 duced on the ware. But cones do not show 

 the temperature below 590° C, e. g., at 200° 

 to 400° C, when the water is given off from 

 the clay, nor can they indicate anything aa 

 to the rate of cooling of a kiln, which is often 

 important in reference to producing, or pre- 

 venting crystallization of the glaze. The main 

 difference between the glaze and the body of 

 the ware is one of fusion temperature; the 

 former fuses completely and is essentially a 

 glass. A good glaze must have proper expansi- 

 bility, to neither chip off nor crack (craze) 

 upon the surface of the ware; and not be at- 

 tacked by water or ordinary acids, especially 

 for culinary ware, and must be hard to resist 

 wear. The ordinary salt glaze on stoneware 

 and the hard glaze on true jwrcelain meet all 

 these conditions, but all other glazes fail in 

 some degree. Four types of glaze are in com- 

 mon use: alkaline or salt glaze, feldspathic, 

 lead, and stanniferous (enamels). The general 

 formula for glaze is xEO, yEjOj 'zSiO^ where 

 HO = sum of metallic fluxes (CaO, MgO, 

 KjO, etc.) ; E.Oj is usually Al^O, or the sum 

 of A10„ Ye.O,, and Cr.O,; some of the SiO, 

 may be replaced by TiO„, SnO„, etc. In the 

 raw glaze, insoluble substances are finely 

 ground and suspended in water, into which the 

 ware is dipped. A fritted glaze has its ma- 



terials partially fused and combined before 

 grinding for the dipping. Thus a fritted 

 glaze is made from soluble substances, or 

 those of high specific gravity which would 

 tend to segregate when the ware is dipped. 

 The fusion of silicates results in the forma- 

 tion of igneous solutions holding the ingredi- 

 ents dissolved, and the temperature of fusion 

 is lowest when several silicates are thus 

 mixed. The more complex glazes and slaga 

 are the most fusible. 



During the afternoon, before the meeting, 

 parties were formed to visit the following 

 manufacturing plants in Worcester : American 

 Steel and Wire Company; Graton and Knight, 

 Tannery and Leather-belting Company; the 

 Worcester Sewage Plant; and the Polytechnic 

 Institute Laboratories and Electrical Engi- 

 neering Building. Later, the members of the 

 Section were entertained at afternoon tea by 

 Professor and Mrs. Leonard P. Kinnicutt at 

 their home on Elm Street. 



Specimens of various kinds of pottery were 

 shown, among which were some from the Art 

 Students' Club of Worcester, and examples of 

 crystalline glazes from the New York State 

 School of Ceramics, at Alfred. 



Prank H. Thorp, 

 Secretary 



THE TORRET BOTANICAL CLUB 



The meeting of April 24, 190T, was called 

 to order at the museum building of the New 

 York Botanical Garden, at 3 :40 p.m., with Dr. 

 M. A. Howe in the chair. Twenty persons 

 were present. 



The following scientific program was pre- 

 sented : 



Ecological Distribution of the Beach and 

 Dune Flora about Chicago, III.: Miss Mary 

 Perle Anderson. 

 - Miss Anderson gave a brief account of the 

 geological history of the ancient Lake Chi- 

 cago and its succession of beaches, the Glen- 

 wood, the Calumet and the Toleston. These 

 ancient beaches were formed by changes in the 

 lake-level, and at the present time are indi- 

 cated by ridges of wooded land more or less 

 parallel to the present coastal beach of Lake 



