EXPERIMENTAL METHODS. 29 



volume. The solution was then ready for analysis. These solutions were a 

 light-brown, color; they were not treated either with lead acetate or blood 

 charcoal, as the amount of error produced by such treatment is equal to or 

 even greater than that produced by the very small amount of protein or 

 tannin substances in the original material. The amount of sugar here 

 found was equal to the hydrolyzed alcoholic extract plus the amount of 

 sugar in the residue from the alcoholic extraction when the former was 

 hydrolyzed and treated in a similar manner. The residue from the alcoholic 

 extraction contained a slight excess of calcium carbonate. It also had to 

 be entirely freed from alcohol before it could be used for the estimation of 

 polysaccharides. For these and several other minor reasons, it was found 

 much more rapid to make these determinations with a fresh sample of the 

 dry material than with the residue from the alcoholic extraction, and it was 

 found that the polysaccharides could be determined accurately from the 

 total sugars by calculation. 



One per cent hydrochloric acid was decided upon for the hydrolysis after 

 considerable experimentation. It was desired to hydrolyze to monosac- 

 charides all those disaccharides and polysaccharides including starch, dex- 

 trine and the mucilaginous substances, which may be important to the plant 

 as reserve food material, but without affecting the cellulose which goes to 

 make up the walls and vessels of the plant. It was necessary, therefore, to 

 utilize the lowest concentration of acid which still hydrolyzed completely 

 the normal reserve materials. Hydrochloric acid affects cellulose less than 

 do other mineral acids of the same ionic concentration. It was found that 

 when the acid mixture was heated for 3 hours on the boiling-water bath a 

 rather definite end-point had been reached ; further prolonged heating and 

 using fresh acid caused exceedingly slight increase in the reducing power of 

 the hydrolyzed mixture. Higher concentrations of acid already seemed 

 to affect the cellulose so that no such definite end-point was obtained ; while 

 still lower concentrations required considerably longer heating in order to 

 completely hydrolyze the starch and other polysaccharides. There was 

 always an odor of furfural in the hydrolyzed mixture, but this was very 

 slight, so that the pentose values were probably affected but very little. 

 With higher concentrations of hydrochloric acid, the furfural was much 

 more noticeable. 



Judging from the microchemical test with iodine, the platyopuntias con- 

 tain an abundance of small starch-grains. When the dried material is 

 mixed with water it takes on the same slimy consistence of the freshly- 

 ground cactus. It was, therefore, impossible to determine the starch 

 chemically by the use of taka-diastase on account of the mucilaginous sub- 

 stances. These can not be filtered through filter-paper even after the addi- 

 tion of much water, and boiling the solution is without effect on them, nor 

 can they be precipitated except by the use of large quantities of alcohol. 

 The clear mucilage which can be obtained by the use of a filter-press always 

 contains considerable starch. 



