and Processes in the Useful Arts. 149 



2. Account of Mr. Dalton's Process for determining the Value of Indigo. 



In order to find the value of any sample of indigo, Mr. Dalton directs us 

 to take one grain, carefully weighed from a mass finely pulverised. Put 

 this into a wine glass, and drop two or three grains of concentrated sul- 

 phuric acid upon it. Having triturated them well, pour in water, and 

 transfer the coloured liquid into a tall cylindrical jar, about one inch in- 

 side diameter. When the mixture is diluted with water, so as to show 

 the flame of a candle through it, mix the liquid solution of oxymuriate 

 of lime with it, agitating it slowly, and never putting any more in till 

 the smell of the preceding portion has vanished. The liquid soon be- 

 comes transparent, and of a beautiful greenish-yellow appearance. Af- 

 ter the dross has subsided, the clear liquid may be passed off, and a lit- 

 tle more water put into the sediment, with a few drops of oxymuriate of 

 lime, and a drop of dilute sulphuric acid ; if more yellow liquid is pro- 

 duced, it arises from particles of indigo which have escaped the action 

 of the oxymuriate before, and must be added to the rest. The value of 

 the indigo Mr. Dalton considers to be in proportion to the quantity of 

 real oxymuriate of lime necessary to destroy its colour. He is of opinion 

 also, that the value may be well estimated by the quantity and intensity 

 of the amber-coloured liquid which the indigo produces, which is found 

 independently of any valuation of the oxymuriate of lime. The following 

 results obtained with several samples, show the great value of this me- 

 thod. 



Oxymuriate of lime used 



to destroy its colour. 



Precipitated and sublimed indigo . . . 140 grains. 



Flora indigo ........ 70 



Another sample ...... 70 



Two other indigos ...... 60 



Two other samples ...... 50 



Another sample ...... 40 



Another sample . . . • • • 30 or 35. 



Mr. Dalton is of opinion, that to destroy indigo by oxyrcmriatic acid, 

 twice the quantity of oxygen is necessary that is required to revive it 

 from the lime solution. See Manchester Memoirs, New Series, vol. iy. 

 p. 437, 438, 439. 



3. Mushet's Process for alloying Copper for Ships. 



In order to increase the tenacity of pure copper, to render it more 

 fibrous, and to prevent the common effects of sea-water upon it, Mr. 

 Mushet has taken out a patent for the following process : — 



He mixes with the copper, as an alloy, regulus of zinc, in the propor- 

 tion of two ounces of zinc to lOOlbs. weight of copper ; or two ounces of 

 block or grain tin ; or four ounces of regulus of antimony ; or eight 

 ounces of regulus of arsenic, in the same quantity of copper. Or, in,. 

 £tcad of employing these substances alone in the above-mentioned pror 

 portions, to lOOlbs. of copper lie proposes to add half an ounce of regu r 



