REPOKT OF CIIEiMICAL LA7iORATORY 
433 
Gommekci.vi, (trades of Sudan Gun 
Tlie following are some commercial grades of Sudan gum obtained from a local firm. 
The grading of gum in the Sudan and Egypt is based primarily upon the size of the tears or 
fragments, the terms used to designate the different sizes being “ bold,” “ large,” “ medium,” 
“ granular,” etc. Grading is, however, also based upon the quality. “ Hard gum ” (called 
in Trieste “Khartoum gum”) is a special grade containing the hard glassy tears which 
exhibit solutions of high viscosity. Since the harder tears do not crush readily in transit, 
and are also usually stronger as regards viscosity of solution, it follows that as a rule the 
grades described as “ bold ” or “ large ” consist of stronger gum. This is not the case with 
bold or large bleached gum, since the variety selected for bleaching in the sun is always 
weaker as regards the viscosity of its solution. In a recent article on the “ Uses, Properties, 
and Production of Gum,” in the Jiullettu of the Imperial Institute (Vol. VI., No. 1), it was 
stated that the comparative weakness of this grade of gum was due to its exposure to the 
sun. This is an error, the actual cause being as stated above. It may be pointed out that 
in many cases the bleaching of these gums is more apparent than real. Exposure to the 
sun results in the drying of the gum to such an extent that it becomes covered with minute 
cracks and fissures, which make it appear much lighter in colour than is actually the 
case. The effect might be likened to the apparent whitening of a piece of yellow glass 
by grinding the surface with emery. 
Where the gum selected for the purpose is already of light colour, the bleaching in this 
way may be made to furnish a gum which dissolves to a practically colourless solution, 
without appreciably injuring its quality in any way except as regards friability. The 
actual advantage of such bleaching is questionable, but as long as the market demands a 
product of this kind it will of course continue to be furnished. It would seem preferable 
rather to select from the gum the tears which are naturally lighter coloured. While such 
selected gum would not have so fine an appearance, it would furnish a solution quite as 
light coloured as ordinary bleached gum, at much less cost for labour, and less attendant 
powdering of the gum, during bleaching and in transit, by reason of the excessive drying. 
Bleaching of strong gum (the hard, glassy form) is not attempted. As already noted, 
the actual reduction in colour due to exposure to the sun is slight, and the dece])tive 
appearance of bleaching due to the formation of minute cracks and fissures does not take 
place with this variety. 
Kordofan gum is sometimes designated in the trade as “ Turkey” gum. 
The term “ sorts ” is used to indicate an ungraded, natural gum. “ All sorts ” is rather 
what is meant. 
The following figures {[lage 434) are not to be relied upon as characteristic of the 
grades in question. “ Medium sifted and cleaned sorts,” for instance, has a higher 
viscosity of solution, not because medium-sized pieces are stronger, but because the given 
lot of gum from which it was selected happened to be of a higher viscosity. 
Generally speaking, all that may be said as regards commercial grades of gum is that 
the so-called hard gum has a solution of higher viscosity and the grades selected for 
bleaching a lower one. The amount of foreign matter is of course materially less in the 
cleaned and selected samples. 
The lower acidity of granular gum and “ siftings ” is probably due to neutralisation by 
alkaline matter in the associated sand, etc., when the sample is brought into solution. 
The grading 
of glims 
Bleaching 
Effect of 
exposure to 
sun 
"Turkey” 
gum 
■' Sorts ” 
