POPULAR SCIENCE KEVIEW. 
o3 
silver, and copper, it says, that “ if after these calces’ 5 (i. c., 
the cyanides or ferrocyanides of gold and silver) “have been 
precipitated, a sufficient quantity of precipitating liquor be 
added, in order to redissolve them, the solution remains clear 
in the open ah’, and in this state the aerial acid 55 (i. e., the 
carbonic acid of the atmosphere) “ does not precipitate the 
metallic calx. 55 
This liquid, “ the precipitating liquor, 55 is obtained by burn- 
ing dried blood with potash in an iron vessel, cooling the 
melted product, and dissolving out its soluble portion by 
water ; the resulting solution contains cyanide and ferro- 
cyanide of potassium, the latter of which is commonly known 
as “ yellow prussiate of potash. 55 
Mr. Wright had been working during several months, ex- 
pressly to obtain a thick deposit of silver, with the aid of a 
separate electric current, before he met with the above passage. 
He then took a solution composed of chloride of silver, dis- 
solved in an aqueous solution of ferrocyanide of potassium, and 
succeeded in obtaining what had never been obtained before, — 
a thick deposit or coating of firm silver by electrolytic action. 
The first article that received the successful coating was a 
small vase, which was coated at Mr. Wright’s residence, and 
the next was a figure of a small kid. The mode of proceed- 
ing adopted by him in these cases, was to place the article in 
the silver solution contained in a porous vessel (a common 
garden-pot), immerse the porous cell in an outer vessel con- 
taining dilute sulphuric acid, place a cylinder of sheet-zinc 
around the porous vessel in the dilute acid, and connect it by 
means of a copper wire with the article to be coated; the 
electrical action then commenced, and the article gradually 
acquired a thick coating of silver : this method is commonly 
known as the “ single cell 55 process.* It was about a month 
after this when a solution of actual cyanide of silver and 
potassium, the substance now universally used for electro- 
plating, was first employed by Mr. Wright for the purpose, 
although cyanides, in several forms, had been used both for 
coppering and silvering by simple immersion, without the aid 
of a battery or zinc, about sixteen months previously. 
The above-mentioned successful results Avere immediately 
submitted to Messrs. Elkington, who made arrangements with 
Mr. Wright for the security of the discovery and invention, 
and patented it on March 25th, 1840; this patent was the 
basis of all successful electro-silver-plating and gilding. A 
handsome remuneration was made to Mr. Wright by this firm 
for his invention, and an annuity paid to his Avidow (afterwards 
* See Plate V. fig. 1, and explanation at end of article. 
