taste or odour—white, yellow, or brown in colour. They are insoluble in water but can be dissolved to a certain extent in alcohol, ether and various oils. Oxygen has not much effect on them with the exception of the copals.
It is very difficult to obtain a pure rosin, it is nearly always a mixture of different rosins, each having separate properties.
One great difficulty to be met with in the making of varnish is that rosins are not always of the same degree of hardness.
This applies to such an extent that various rosins are classified under two heads, namely, hard and tender.
Under the heading of hard we have copal, shellac and amber. The name tender is given to such rosins as sandarach, mastic and dammar.
But there are some copals which are neither hard nor tender, but are what might be termed semi-hard. It is difficult in spite of these descriptions to obtain in the trade an article that will correspond accurately to the various requirements that may be needed.
Gum Arabic.—There are numerous varie-
