[ 191 ] 



XXXV. Comparative Examination of the Mucous Acid 



formed by the Action of the Nitric Acid: \st 9 on the 



Gums; Qdly, on the Sugar of Milk. ByM. Laugier*. 



JYjL Vauquelin ascertained by his experiments on gam 

 arabic and gum tragacanth the existence of a very consi- 

 derable quantity of lime in these substances. 



The perusal of his experiments suggested the following 

 reflections : — 



1. What becomes of the lime contained in these gums 

 when we treat them by the nitric acid^ with the view of 

 procuring mucous acid ? 



2. Is it not combined with the oxalic acid which is 

 formed almost at the same time with the mucous acid ? 



3. The oxalate of lime being more insoluble in water 

 than the mucous acid, is it not precipitated with this acid, 

 when we wash the residue after the operation ? and does it 

 not alter in a sensible manner its properties ? 



4. What ought to be the means of ascertaining the pre- 

 sence of the oxalate of lime in the mucous acid obtained 

 from the gums, and of separating this calcareous salt from 

 the acid whose purity it injures? 



With a view to resolve these questions, I undertook the 

 following experiments : 



I digested with eight parts (480 grammes) of pure nitric 

 acid at 360° one part (60 grammes) of gum tragacanth ; 

 I heated the mixture until it was reduced into a honey-like 

 substance, and I added a sufficient quantity of water. 



The latter would not dissolve a white pulverulent matter, 

 which I gathered on a filter, and which when dried in the 

 air weighed {) grammes and a half, and this was mucous 

 acid. The liquor containing the soluble portion of the 

 mixture was of a yellow colour. I evaporated it, and did 

 not take it from the fire until I saw if covered with a slight 

 pellicle which was formed at its surface : by and by, upon 

 cooling, the liquor deposited a great quantity of crystals,, 

 some in lamince, others in needles very well defined as 

 oxalic acid. With the view of separating this last acid 

 from the mucous acid, I poured upon the mixture alcohol 

 at 40°, which dissolved the oxalic acid without touching the 

 mucous acid which I collected on a filter. The second 

 portion of mucous acid weighed two grammes 0*]0. The 

 .alcoholic solution furnished, on a gentle evaporation, a co- 



• Anmi-Ui de Chimie, tome Ixxii. p. 81. 



loured 



