246 Reaction of Sulphuric Acid. 



I have applied to the directors of the British Institutions, Pall 

 Mall, to permit one or two of these Tapestries to be exhibited with 

 the old masters in June ; thus those who saw them last year, 

 may be able to see what they now are, and both science and art 

 may be served ; for a comparison has never yet been made, since 

 the Cartoons were repaired and painted upon, with the tapestry. 



I think, Sir, you will recollect my subject of the stoning St. 

 Stephen, the large masses of blue cloud-like appearance hanging 

 about and over Jerusalem : these have nearly disappeared, and 

 mountain scenery taken the place ! The olive grove, which only 

 showed a few trees in front all blue, and a heavy blue-like cur- 

 tain was over all of the grove ; the curtain has disappeared, and 

 a fine deep grove is now seen ; the natural green and mossy bank 

 have nearly taken their original state ; fresh lights keep breaking 

 out and showing even deeper in the grove ! and throughout the 

 works, the original lights are working their way, from the heavier 

 color. I remain, Sir, yours, &c., 



Wm. Trull. 



Art. VII. — Of the Reaction of Sulphuric Acid with the Essential 

 Oil of Hemlock ; by Clark Hare, of Philadelphia.* 



If equal parts of sulphuric acid and oil of hemlock be mingled 

 together, refrigeration being employed to prevent too great a rise 

 of temperature, a black acid resinous mass results. By the addi- 

 tion of carbonate of lead and water, the unaltered sulphuric acid, 

 present in great quantity, is converted into an insoluble sulphate, 

 which, mingling with the resin, gives rise to a yellow mass re- 

 sembling putty in its consistency, while there will be found dis- 

 solved in the water two soluble salts of lead. 



The presence of a very large quantity of coloring matter, inter- 

 feres with the examination of these salts. This, however, in a 

 great measure disappears on precipitating the lead by sulphydric 

 acid gas, resaturating the liberated acids by the carbonate, and 

 again throwing down the lead in the state of a sulphide. The 

 partially decolorized acids thus obtained may then be saturated 

 with barytes, and the resulting salts evaporated to dryness, when 

 they assume the appearance of an amorphous mass. By washing 



* Eldest son of Dr. Hare. 



