116 On the Manufacture of Glass. 



The lime is changed to an hydrate and likewise sifted. 

 The potash is broken into pieces not larger than a walnut. 

 The salt needs no preparation. 



Kelp. — This term is applied to a salt made from the 

 ashes, collected from under the kettles of the salt works at 

 Salina. It is manufactured in the same manner as potash, 

 by lixiviation and evaporation. It is used in our manufac- 

 tory as a substitute for salt and potash. I should think it a 

 compound salt, composed of muriate of potash and carbon- 

 ate or sub-carbonate of soda, in nearly equal proportions. It 

 would be preferable to potash in the formation of glass, 

 could we always rely upon its composition ; but this at times 

 varying, causes occasionally serious loss. 



The sulphates of potash and soda, when employed, should 

 be finely pulverised. The saw dust is used as being more 

 convenient than charcoal. The effect of either is to decom- 

 pose the sulphates, by seizing the oxygen of the sulphuric 

 acid, forming carbonic acid, and escaping through the mate- 

 rials, while the sulphur of the sulphuric acid, being left free 

 is driven off by the heat employed, and the alkali remains 

 in its purest form, to unite with the silex. 



The materials being prepared as above stated, are put to- 

 gether, and so intimately blended, thai the different articles 

 shall be uniformly distributed through the whole mass. If 

 circumstances will permit, it should remain three months in 

 this condition. 



There is but a slight difference in the quality of the glass 

 which these different mixtures produce, and the time requir- 

 ed for their fusion is nearly the same. As to the relative cost 

 of either, it must depend upon the comparative price of the 

 several articles in market, which of course varies from time 

 to time. 



Sometimes, in consequence of the materials not being 

 sufficiently free from vegetable impurities, the glass will as- 

 sume a yellowish tinge. To obviate this, or to correct it 

 when it occurs, the white oxid of 'arsenic, the black oxid of 

 manganese, the nitrate of potash and the oxides of lead are 

 all occasionally used. They all appear to act, by furnishing 

 oxygen, which combining with the carbon, carries it off in 

 the form of carbonic acid gas. 



To get these materials to the bottom of the pots, that they 

 may unite with the glass, and produce the intended effect, is 

 best accomplished by wrapping them in a wet paper, and 



