428 Progress in Science. [July* ^7^- 



the powder, first with dilute caustic potassa, and, after filtration and addition 

 of a large quantity of pure water, a solution of iodine is added, whereby the 

 starch is detected. 



TECHNOLOGY. 



The Boston "Journal of Chemistry " gives the following interesting account 

 of the way in which the natives of East India clean silver articles : — Cut some 

 juicy lemons in slices ; with these rub any large silver or plated article 

 briskly, and leave it hidden by the slices in a pan for a few hours. For delicate 

 jewellery, the Indians cut a large lime nearly in half, and insert the orna- 

 ment ; they then close up the halves tightly, and put it away for a few hours. 

 The articles are then to be removed, rinsed in two or three waters, and con- 

 signed to a saucepan of nearly boiling soapsuds, well stirred about, taken out, 

 again brushed, rinsed, and finally dried on a metal plate over hot water, 

 finishing the process by a little rub of wash-leather (if smooth work). For 

 very old neglected or corroded silver, dip the article, with a slow stirring motion, 

 in a rather weak solution of cyanide of potassium ; but this process requires 

 care and practice, as it is by dissolving off the dirty silver you obtain the 

 effect. Green tamarind pods (oxalate of potash) are greater detergents of gold 

 and silver articles than lemons, and are much more employed by the artisan 

 for removal of oxides and fire-marks. 



According to P. Rast so-called German silver may be applied to soldering 

 steel to iron and iron to copper. Borax should be used as a flux, and the 

 German silver granulated as is done for hard brass solder. 



Iron may be gilded by first applying sodium amalgam to the iron, which is 

 thereby readily coated with mercury. Next a concentrated solution of chloride 

 of gold is applied to the mercurially coated surface ; and lastly, the object is 

 strongly heated, either in a muffle or in the flame of an enameller's lamp. 



Common mercurial ointment has been found remarkably efficacious in pre- 

 venting the formation of rust upon articles of iron and steel, such as gun- 

 barrels. 



%* The article in No. xxxviii. of the " Quarterly Journal of Science" on 

 " Atmospheric Life Germs " was written by Mr. W. N. Hartley, of King's 

 College, whose name was inadvertently omitted. 



