1819.] Scientific Intelligence. 315 



in a common red heat. I had precipitated a carbonate of zinc, 

 by dissolving common zinc in muriatic acid, and mixing the 

 neutral solution with carbonate of soda. To convert this car- 

 bonate into oxide of zinc, I dried it in the open air, and then 

 exposed it to a strong red heat in a platinum crucible covered 

 with a lid. When the process was at an end, I found the inside 

 of the lid coated with a substance resembling massicot. By- 

 digesting the lid in dilute nitric acid, I dissolved off the subli- 

 mate, and by evaporation obtained octahedral crystals of nitrate 

 of lead. This unexpected fact induced me to visit a manufac- 

 tory in Glasgow, where lead is reduced from galena, and after- 

 wards converted into litharge. The volatilization of the lead in 

 both processes was apparent ; and I found on inquiry, that the 

 workmen were quite aware of it. I have been told, that when 

 lead is converted into litharge, and the litharge again reduced 

 into lead by the common method, that the loss sustained rather 

 exceeds 10 per cent. 



VIII. Queries respecting the Velocipede. 



(To Dr. Thomson.) 

 SIR, 



As your journal embraces mechanics within the range of its 

 notice, I am a little surprised that so curious and popular an 

 invention as the Velocipede should have been hitherto over- 

 looked. It is now about a year since I saw these whimsical 

 machines in full action under the trees in the Jardin de Tivoli at 

 Paris. I then anticipated the probability of their being converted 

 to purposes of expedition; and accordingly on my return to 

 England, a few months ago, I found them running everywhere 

 throughout the kingdom. It is not because they are uncommon, 

 therefore, that I now beg to call your attention to them ; but it 

 appears to me to be right that some account of the invention, 

 with the improvements that have been made on it, should be 

 registered in the contemporaneous numbers of a permanent and 

 respectable journal. I hope, therefore, that you, Sir, or some 

 of your mechanical correspondents, will favour us with an 

 accurate description and plate of the machine, together with 

 some remarks on its powers, and the improvements of which it 

 is capable, as well as in the mode of working it. I regret to 

 understand that it has frequently produced hernia in those who 

 have exercised themselves with it. I should think this extremely 

 probable ; but it might be well that the fact were generally 

 known. I am, Sir, &c. 



T. L. D. 



