400 Professor T. E. Thorpe [May 4, 



distressing nature of lead poisoning ; of the total or partial paralysis, 

 sometimes ending in death, to which it gives rise ; of the blindness, 

 debility, and prolonged misery which, even in its less acute forms, it 

 occasions. Nor do I care to dwell upon the statistics the authorities 

 have been able to collect respecting its prevalence. It is sufficient to 

 say that it is allowed by all to have existed to an extent which con- 

 stitutes a grave reflection upon the conduct of one of the most 

 important of our staple industries, and public sentiment has demanded 

 that some steps shall be taken to remove the evil. 



A very few words will serve to explain to you how the mischief 

 arises. Without attempting to be comprehensive or to enter into too 

 great detail, I may say that, broadly speaking, the articles of pottery 

 with which I shall concern myself to-night, in order to explain the 

 position, group themselves into the two main classes of earthenware 

 and china or porcelain. 



Earthenware is made of a mixture of so called ball-clay, china- 

 clay, china-stone, and flint. The ball-clay and china-clay are sub- 

 stantially more or less pure silicate of alumina, derived from the 

 decomposition of felspar; the china-stone is a silicate of alumina 

 containing more or less undecomposed felspar ; and flint is practically 

 pure silica. These substances, in various proportions, and intimately 

 commingled, constitute the paste from which the article of earthen- 

 ware is fashioned. The various modes of fashioning the article, 

 whether by throwing on the wheel, pressing, or casting, I need not 

 stop to explain. 



The articles so made, after a preliminary drying, are packed in 

 large earthenware vessels made of fireclay, technically known as 

 " saggers," and are heated to a temperature, depending on their 

 nature, in an oven. In this form the fired ware is known as 

 '• biscuit." It is hard and sonorous, but is pervious to liquids, 

 and on account of its slightly roughened surface, would rapidly 

 collect dust, and thereby become soiled. For most purposes, there- 

 fore, it requires to be glazed — that is, coated with some sufficiently 

 fusible material capable of rendering it impervious to liquids. 



The greater part of the porcelain made in this country is of the 

 variety known as soft-j)aste porcelain, and differs essentially from 

 that made in China or in various Continental countries. Chinese 

 and Continental porcelains consist mainly of mixtures of china-clay 

 and felspar. English porcelain is composed of china-clay and china- 

 stone, mixed with nearly their joint weight of bone-ash or phosphate 

 of lime. The English porcelain or bone " biscuit," like earthenware 

 " biscuit," is pervious to liquids, and therefore requires to be glazed. 



The glazing of both varieties is done in substantially the same 

 manner — that is, the articles are dipped in a thin cream-like fluid 

 containing, in a state of suspension, finely divided double silicates, 

 or silico-borates of alumina, alkalis and alkaline-earths, associated 

 for the most part with lead compounds in amount often reaching to 

 half the weight of the glazing material. 



