^-825 .J , Scientifich NoticeS'^Chemist?^. 7^ 



once a sojution of pure potash, without the additional trouble of 

 evaporation and solution in alcohol ; and we obviate the recon- 

 version of the alkali into carbonate, which always happens dur- 

 ing the evaporation in the common process, unless the tedious 

 and troublesome method of evaporating without contact of the 

 atmosphere be adopted, in which case silver vessels become 

 necessary. 



As a test to ascertain whether or not a solution of potash be 

 perfectly caustic, chemists make use of a dilute acid ; but this 

 method gives no information unless the acid be added in excess. 

 A small quantity will only displace the carbonic acid from one 

 portion of potash ; but the remaining portion will unite with the 

 liberated acid so as to prevent any appearance of effervescence. 

 Thus an .alkali that is in fact partly carbonated will not be 

 affected apparently by the affusion of a small quantity of a test 

 acid.r — (Dubhn Philosophical Journal.) 



2. Account of Mr, Dallon'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 amass finely 

 pulverised. Put this into a wine glass, and drop two or three 

 grains of concentrated sulphuric acid upon it. Having triturated 

 them well, pour in water, and transfer the coloured liquid into a 

 tall cylindrical jar, about one inch inside 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 hquid soon becomes 

 transparent, and of a beautiful greenish yellow appearance* 

 After the dross has subsided, the clear liquid may be passed off,, 

 and a little 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 produced, 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 inten- 

 sity 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 method. 



Oxymuriate of lime used to 

 destroy its colour. 



Precipitated and sublimed indigo 140 grains 



Flora indigo ,..,.. 70 - 



