FERMENTATION OF CELLULOSE 161 



soluble starch, the starch cellulose enveloping the starch 

 granules was destroyed by digesting with dilute hydrochloric 

 acid. 



Allied with cellulose are kindred bodies belonging to the 

 pectin group. 



Pectose is the name given to the parent substance of bodies 

 such as pectin, pectic acid, etc. 



Pectin can be obtained by filtering the juice of a ripe 

 apple or pear through muslin, and adding an equal bulk of 

 alcohol. The pectin is precipitated as a stringy gelatinous 

 mass, which can be reduced to a white powder soluble in 

 water. 



A solution of pectin gelatinises on standing, probably 

 by the action of the enzyme pectase contained in the fruit 

 juice. 



The members of the pectose group have chiefly been in- 

 vestigated by the French chemist Mangin, who divides these 

 bodies into two series : 



(1) Neutral bodies which vary in their solubility in 

 water. At one extreme we have the substance pectose, which 

 is insoluble in water and closely associated with cellulose ; at 

 the other extreme the substance known as pectin, which is 

 soluble in water but tends to form a jelly fairly readily. Inter- 

 mediate between these are bodies of a gelatinous nature. 



(2) Substances allied to this group are feeble acids, the 

 chief member being pectic acid, which occurs as calcium 

 pectate ; the latter forms a binding substance between the 

 fibre of many plants. 



Pectose bodies differ from cellulose derivatives in being in- 

 soluble in Schweitzer's reagent. This is obtained as follows : 



A saturated solution in water is made of equal parts of 

 copper sulphate and ammonium chloride. Strong caustic soda 

 is added till no further precipitate is formed. This precipi- 

 tate of hydrated copper oxide is dissolved in strong ammonia 

 solution as required. 



