392 Miscellaneous InteUigeiire. 



The tube was, lastly, filled alternately with sulphuric and 

 muriatic acid, and a discharge made through them when the 

 electrometer indicated 80° of intensity, at which the gun- 

 powder would not take fire. 



Should you consider any of the foregoing experiments of im- 

 portance, I shall leave you to make what use of them you may 

 think proper. I am, SjX. 



Rotherhithe,2Ath May, \82\. J. Leuthwaite. 



11. Use of Chromate of Lead as a Dye.— The following ob- 

 servations on this subject are by M. Berthier : " The chromate 

 of lead applies very well on stuiFs, and I have many times 

 repeated the experiment. The following are some remarks I 

 have made. 



" With subacetate of lead and neutral chromate of potassa, 

 only an orange colour is obtained, not very agreeable ; but if 

 the stuffs thus dyed be dipped in acetic acid, they almost im- 

 mediately acquire a very fine and brilliant yellow lemon colonr. 

 On using the neutral acetate of lead in place of the subacetate, 

 a fine gold colour is immediately obtained, with the chromate of 

 potassa, but acetic acid cannot give it the yellow lemon colour. 



" These colours are absolutely unalterable by soap and water 

 when cold ; at boiling temperatures they fade a little, without 

 any change of tint, but vinegar restores their first brilliancy. 



" Ammonia makes them of a red orange colour ; acetic acid 

 restores them to their primitive state. When chromate of lead 

 is treated by ammonia, it may be made to pass through a 

 great variety of shades from orange to the red of the finest 

 minium. The ammonia in these cases dissolves chromic acid, 

 and leaves a red chromate. The action of acid, either nitric or 

 acetic, is to dissolve oxide of lead from this chromate, and 

 leave the clear yellow compound. 



" Stulfs dyed by the chromate of lead, have their colours im- 

 mediately and completely destroyed by the subacetate of soda 

 and by muriatic acid, even when cold." — Annales des Mines, 

 vi. 137. 



12. Porcelain Glaze. — Mr. Rose, of Coalport, Shropshire, 

 has sent a communication to the Society of Arts, in which a 

 new glaze for porcelain is described. The object was to pro- 

 duce a glaze containing no lead, so that colours afterwards 

 laid on to, and burned into, it, should not be altered by that 

 metal. 'Ihe principal ingredient in it is feldspar, of a some- 

 what compact texture, and a pale flesh red-colour, which forms 

 veins in a slaty rock, adjoining to the town of Welchpool, in 

 Montgomeryshire. This material being freed from all adhering 

 pieces of slate and quartz, is ground to a fine powder ; and, 

 being thus prepared, 27 parts are mixed with 18 of borax, 4 of 



