61 E. Linebarger — Molecular Masses of Dextrine, etc. 427 



having the formula when dried at 1.00° (C 12 H M O n ) M . Nothing 

 positive is known as to the numerical value of n. Let us see 

 if Pfeffer's measurements will give us some information. 



Pfeffer found that a 1 per cent solution of gum arabic* 

 exercised an osmotic pressure of 7 , 2 cm of mercury at 16"1°. 

 Applying the formula for dilute solutions, pv = RT, where p 

 indicates pressure in grms. per cm 3 , v the volume occupied by 

 a molecule of the dissolved substance, R the constant, 84500, 

 and T the absolute temperature, we have p = 97*2 grms. per 

 cm 3 , T = 289*1° and v = 100 x, where x represents the molecular 

 mass of gum arabic. On solving, we obtain for x the value 

 2513. This can be regarded as only approximately correct, for 

 probably the gum arabic employed was not chemically pure. 

 Now the molecular mass of a substance possessing the formula 

 C 12 H 22 O n is 342, which multiplied by seven gives 2394. This 

 does not differ greatly from the value obtained by experi- 

 ment. As gum arabic when ignited leaves an ash amount- 

 ing to 3-4 per ceut of its weight and consisting of the carbo- 

 nates of potassium, magnesium and calcium, the formula to be 

 ascribed to the gum is not (C i2 H 22 O u ), but a similar one in 

 which some of the hydrogen atoms are replaced by the above 

 bases. This would so increase the molecular mass that it 

 would approach nearer that found experimentally. We con- 

 clude then that the molecular mass of gum arabic is about 

 2500, and that the molecule consists of seven simpler mole- 

 coles. 



For dextrine, f Pfeffer found in 1 per cent solution an 

 osmotic pressure of 16*6 cm of mercury at 15*6° C. Applying 

 the formula, we have T = 288'6°, p = 2254. grm. per cm 3 and 

 v = 100 x, solving, x = 1083. A substance of the formula 

 C 6 H ]0 O 5 has a molecular mass of 162 ; multiplying by seven, we 

 obtain 1134, a number which agrees well with the one obtained 

 by experiment. The molecular mass of dextrine is therefore 

 1134 and its formula (C 6 H 10 O 5 ) 7 . 



I recently"!; published the results of the determination of 

 the osmotic pressure exerted by colloid tungstic acid, from 

 which the molecular mass was calculated to be 1750 and the 

 molecule (H 2 W0 4 ) 7 . It is remarkable that in these three cases, 

 which as far as I know, are the only ones yet examined, the 

 colloid molecule is seven times the simple molecule. This 



*The gum arabic is stated as being "Bei 100° C. getrocknetes arabisches 

 Grummi." Osm. Unt., p. 105. 



f The following is the description of the dextrine employed. " Das Dextrin 

 war als chemisch rein von der Fabrik bezeichnet. Da ion (Pfeffer) es aber nicht 

 einer speciellen fieimgung unterwarf. so kauri ich nur sagen, class Traubenzucker, 

 wenn iiberhaupt darin vorhanden, jedenfalls nur in minimaler MeDge zugegen 

 war." Osm. Unt, p. 112. 



% In March number of this Journal, cxliii, 218. 



