CONTRIBUTIONS TO BLOWPIPE ANALYSIS. 343 



indefinite greyish-brown colour. If some oxide of manganese be 

 fused with carbonate of soda so as to produce a greenish-blue bead or 

 " turquoise enamel," and some baryta or a baryta salt be melted into 

 this, the colour of the bead will remain unchanged ; but if strontia be 

 used in place of baryta, a brown or greyish-brown enamel is produced. 

 NoTK : — Some examples of Witherite, Barytine, and Baryto-calcite, 

 contain traces of oxide of manganese. These, after strong ignition, 

 often assume per se a pale greenish-blue colour. 



5. DETECTION OF BARYTA IN THE PRESENCE OF 

 STRONTIA. 



[First published in the Chemical Gazette : August 1, 1846.] 



This test is chiefly applicable to the detection of baryta in the 

 natural sulphate of strontia ; but it answers equally for the examina- 

 tion of chemical precipitates, &c., in which baryta and strontia may 

 be present together. The test-matter, in fine powder, is to be 

 melted in a platinum spoon with 3 or 4 volumes of chloride of calcium, 

 and the fused mass treated with boiling water. For this purpose, the 

 spoon may be dropped into a test-tube, or placed (bottom upwards) 

 in a small porcelain capsule. The clear solution, decanted from any 

 residue that may remain, is then to be diluted with 8 or 10 times its 

 Tolume of water, and tested with a few drops of chromate (or bi- 

 chromate) of potash. A precipitate, or turbidity, indicates the pres- 

 ence of baryta. 



6. ACTION OF BARYTA ON TITANIC ACID. 



[First published in Chemical Gazette : 1852. 



Fused with borax in a reducing flame, Titanic acid forms a dark 

 amethystine-blue glass, which becomes light-blue and opaque when 

 subjected to the flaming process. The amethystine colour arises from 

 the presence of Ti^O^ : the light-blue enamelled surface, from the 

 precipitation of a certain portion of TiO^. The presence of baryta, 

 even in comparatively small quantity, quite destroys the latter reaction. 

 "When exposed to an intermittent flame, the glass (on the addition of 



