PECTIC ACID.

43

:heil

that

by

of

so

the

the

will

is

of

by athatpre-withveryisticom-verytateasofatertheand

y a

ing

rich

of

it

was

ate.

tion

der,

was

cid,

ted.

xed

Dre-

and

was

h aiodch,als

possessed the properties of tyrosine, and were quite free from leucine. Nowas tyrosine is only formed, as far as we know, from albumen and bodies of thesame class, it is almost certain that cotton contains a small quantity ofan albuminous substance. The oxalic acid obtained in this experiment wasdoubtless derived from the pedtic acid. Of the ratio in which the latter standsto the albuminous matter, some estimate may be formed by that subsistingbetween their respective products of decomposition.

The precipitate produced by acid in an alkaline extract of cotton contains,then, the following organic substances :—

1. Cotton wax.

2. Margaric acid.

3. A colouring matter easily soluble in alcohol.

4. A colouring matter sparingly soluble in alcohol.

5. PeCtic acid.

6. Albuminous matter.

Of these various bodies the peCtic acid far exceeds the others in quantity.Then follow the colouring matters. The three other constituents are presentin extremely minutes quantities only. Dr. Schunck thinks it possible thatcotton fibre may contain, besides these, other organic substances whichare soluble in water or alkali, but are not afterwards precipitated by acid.It is well known that cotton, during the process of bleaching, loses about5 per cent of its weight, whereas the total weight of all the substances obtainedin Schunck’s experiments amounts to hardly | per cent. It is, however, notimprobable that a portion of the matter which escaped observation may con-sist in great part of parapeClic acid. This body, though insoluble in tolerablystrong acids or saline solutions, is soluble in pure water. When, therefore, itis precipitated from an alkaline solution, the precipitate, on being filtered offand washed, begins gradually to dissolve as soon as the greatest part of theprecipitant has been removed. This was observed on washing the precipitatethrown down by acid from the alkaline extradt of cotton. When the acid hasto some extent been removed, the wash-water begins to becomes thick andslimy, and runs through very slowly, in consequence of its dissolving a portionof the parape&ic acid of the precipitate. A part also of the pedtic acidoriginally present may undergo a further change by the adtion of the alkali,and be converted into the metapedtic acid of Fremy, which is very soluble inwater, and is not precipitated by stronger acids. The loss of weight sustainedby cotton during its treatment with alkali, and not accounted for by Schunck’sexperiments, may therefore be due to such derivatives of pedtine as are not pre-cipitated by acid, or are subsequently removed by washing the precipitate withwater.