AUSTRALIAN VEGETABLE EXUDATIONS, ° 395 
consists principally of the lime and magnesia salts of arabic acid, 
as the arabin, when precipitated from its solution by alcohol, 
heated with dilute sulphuric acid, the acid solution neutralised by 
carbonate of lime, then precipitated with hot alcohol, yields a 
filtrate which when evaporated to a syrup, gives arabinose. 
The portion dissolved by dilute soda solution was metarabin, as 
when dissolved it changes into arabin. This is precipitated from 
the alkaline solution by the addition of alcohol. This precipitate — 
when filtered off, washed with alcohol, dissolved in water, acidified, 
and again precipitated by alcohol has all the appearance of arabin. 
When this precipitate is heated with dilute sulphuric acid, treated 
in the usual way (above described), a crystallized sugar is obtained 
having the rhombic character of arabinose, and which when dis- 
solved in water is dextro-rotatory. This gum may therefore be 
considered as belonging to the arabin group, the portion not 
soluble in water being metarabin. 
This gum contained 17:23 per cent. of moisture, while the per- 
centage of ash was only 1:94, which is low fora gum. ‘The ash 
consisted of the carbonates of lime and magnesia, and a small 
quantity of potassium; it also contained both sulphuric and phos- 
phoric acids. The colour of the ash is white. It contains a small 
percentage of albuminoids, as the presence of nitrogen was readily 
detected by the ordinary method. 
When heated with strong nitric acid a large quantity of mucic 
acid is formed; as much as 29-98 per cent. was obtained from this 
specimen. The method followed in estimating the mucic acid in 
these gums, is to treat about two grams. of the powdered gum with 
about 8 cc. of nitric acid in a beaker, gently heating until a clear 
Solution is obtained. The heat is then slightly increased until 
the greater portion of the acid is driven off; the remainder 
becomes turbid. After standing some hours, to allow erystalliza- 
tion to take place, about 5 cc. of nitric acid is added, the mucic 
acid filtered off, washed with water, dried and weighed. The 
filtrate (with the washings) is evaporated down, again treated 
