[ 401 ] 



LV. On the Composition and Phosphorescence of Plate-sulphate 

 of Potash. By Dr. Frederick. Penny, Professor of Chemistry, 

 Andersonian University, Glasgow^'-. 



THE subject of the present notice is a teclmical product from 

 kelp. It is called " Plate-sulphate of Potash/^ and is so 

 named from the circumstance of its being crystallized in thick 

 plates or slabs, consisting of the aggregrated layers of successive 

 crops of crystals. 



It may be regarded as one of the chemical products peculiar 

 to Glasgow, being manufactured only at one or two other places, 

 and even there to a limited extent. 



There are several points in the chemical history of this salt 

 possessing a high degree of scientific interest. The most im- 

 portant are, the peculiarity of the process by which it is obtained 

 in thick slabs or ])lates, the brilliant phosphorescence of its cry- 

 stals at the time of their formation, and its remarkable compo- 

 sition. To these at least I shall limit my remarks in the present 

 notice. 



I. Formation of the Plate-sulphate. 



In working kelp upon the large scale, several saline products 

 are obtained, and among these there are two salts, containing 

 sulphate of potash as the predominating ingredient. One is 

 powdery or granular, and is distinguished as soft or granulated 

 sulphate of potash, and the other is the /j/«/e-sulphate. 



Soft sulphate is obtained by simply evaporating or concentrating 

 the kelp-leys, when it falls as a heavy granular precipitate. It is 

 a very impure substance, being largely intermixed with sulphate 

 of soda, coumion salt, carbonate of soda, sulphocyanide of potas- 

 sium, iodide of sodium, and with insoluble matter and water. 

 The amount of sulphate of potash existing in soft sulphate is 

 very variable. That from cut-weed kelp seldom contains more 

 than 32 per cent. Good drift-weed kelp yields a sulphate not 

 usually under 44 per cent., and occasionally as high as 65 per 

 cent. It is used in making plate-sulphate, and for agricultural 

 manures, particularly wlien of low strength. 



Plate-sulphate is made in two ways : either from the impure 

 soft sulphate, or directly from the liquors that result by steeping 

 kelp in hot water. The process is called "plating," and the 

 mode of working is peculiar. In the ordinary process of crystal- 

 lizing salts by solution in water, each crop of crystals, when fully 

 formed, is removed from the crystallizing vat or vessel after the 

 mother-liquor has been run oft"; a second or third crop being 

 obtained by evaporating the mother-liquor, or by dissolving iu 



* Communicated by the Author. 



