188 ON THE DECOMPOSING POWER OF HOT STEAM. 
form combinations which are fixed,and by this means their 
sahs come under the above rule." 
The facts developed by Tighlmau tend to explain many 
geological phenomena of volcanic character, especially the 
evolution of boracic and silicic acids in Tuscany and Iceland, 
and will doubtless lead to many other important results of 
a purely scientific connection. 
Having before me an official copy of the Letters Patent 
granted by the British government to Richard Albert Tighl- 
man, on the 1st of February, 1847, giving him the full 
right and power to manufacture under the same, as well as 
some letters from the patentee, exhibiting the efforts that 
have been made towards perfecting the practical working 
of his processes. I will give such parts of them as will 
prove of interest. 
The first patent embraces the right to make certain salts 
of potash, as the sulphate, chloride and chromate, from fel- 
spars containing that alkali, and the proportions mentioned 
, in the patent are intended for a felspar containing sixteen 
per cent, of potash. To obtain sulphate of potash, two 
parts by weight of^ felspar, one part of lime, or an equiva- 
lent quantity of carbonate of lime, and one part of sulphate 
of lime, (or sulphate of strontia or baryta, though the lime 
salt is preferred,) all reduced to fine powder, are intimately 
mixed, placed on the hearth of a reverberatory furnace, and 
kept at a bright red heat for eight hours, the mixture being 
stirred from time to time, that all parts may be equally 
heated. The sulphate of potash forms most rapidly at a high 
temperature, but the heat must not be sufficient to cause 
fusion, else the subsequent process of extraction, will be 
materially interfered with. It is also necessary that the 
atmosphere of the furnace should not be deoxidizing so as 
to injure the product, to regulate which, the furnace is con- 
structed with openings above the fuel, to admit sufficient 
air, so as to keep the atmosphere at a proper oxidizing con- 
dition. The heating is continued for about eight hours, the 
