L. TECHNOLOGY. 465 



ides of lead, or insoluble basic salts of lead, in the two fol- 

 lowing ways : First, by mixing litharge, hydrated oxides of 

 lead, or insoluble basic salts of lead, with an equivalent of 

 bicarbonate of soda, together with sufficient water to form a 

 stiffish paste. This mixture is to be ground in a suitable 

 mill, small quantities of water being from time to time add- 

 ed, as may be found requisite, until the change of the lead 

 bodies into carbonates is complete. The paste is to be well 

 washed with water, and the supernatant liquid, which con- 

 tains mono-carbonate of soda, is separated from the white 

 lead by filtration, and is boiled down to dryness, and disposed 

 of as soda ash, or it may be crystallized, or may be again con- 

 verted into bicarbonate of soda by treatment with carbonic 

 acid, and used to convert further quantities of lead oxides 

 or insoluble basic salts of lead into carbonates. Instead of 

 grinding the lead oxides or insoluble basic salts of lead into 

 a fine state of division, they may simply be mixed with bi- 

 carbonate of soda and water, and left to themselves, when 

 the conversion into carbonates goes on in the same manner, 

 only much more slowly. Secondly, by mixing hydrated ox- 

 ides of lead or basic salts of lead with caustic soda, mono- 

 carbonate of soda, or acid carbonates of soda, and sufficient 

 water, a stiffish paste is formed. The mixture is then intro- 

 duced into a closed mill, and during the grinding a stream 

 of carbonic acid gas passed into it. After the conversion of 

 the lead bodies into carbonates they are washed with water, 

 and the supernatant liquid treated as before mentioned. 3 A, 

 April 8,260. 



duckham's self-indicating weighing machine. 



The London Mechanics'' Magazine for August 19 gives a 

 figure of what it considers a very important mechanical im- 

 provement, namely, Duckham's Self-indicating Hydrostatic 

 Weighing Machine. This consists essentially of an open-top 

 cylinder filled with water or oil, and fitted with a water-tight 

 piston and pressure-gauge, and when used for weighing goods 

 is simply interposed between the crane on which they are 

 suspended and the goods themselves. The indicator on the 

 dial-plate turns as the object is lifted, and the weight is read 

 off at once, the work being accomplished with the utmost 

 celerity and accuracy. The machine is in use at the Royal 



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