In the American and Japanese species they are a mixture of catechol and pyrogallol tannins, while they appear to be pure pyrogallol tannins in the Chinese species.
In the Chinese trees all the tannins of the bark belong to the toxic pyrogallol groups, and this, combined with their high solubility, results in the high degree of resistance in this species (4).
Thus the "maximum luminescence pressure" of pyrogallol increases with increase of temperature.
However, as we have seen, not lowering but raising the temperature causes luminescence with high oxygen concentration or high pyrogallol concentration.
The blackening of pyrogallol with absorption of oxygen in presence of alkali is a very well-known reaction, but luminescence does not accompany this type of oxidation.
Of course with high active mass of oxygen (in case of phosphorous luminescence) or of pyrogallol (in case of pyrogallol luminescence) the reaction velocity must be greater than the optimum.
A somewhat analogous case is presented by the oxidation ofpyrogallol solution in contact with ozone, except that in this reaction too high a concentration of pyrogallol will hinder the oxidation.
Table 10 shows the relation between temperature and intensity of luminescence with pyrogallol and various oxidizers.
If the pyrogallol is of m concentration, no luminescence occurs at 0 deg.
The Oxidizer is Mixed with an Equal Amount of M/100 Pyrogallol + 3 per cent.
TABLE 7 Peroxides Giving Light with Pyrogallol and Oxidizers Key to column headings: [A]: Oxidizer.
Of the trihydroxybenzenes pyrogallol and phloroglucinol only were included in these investigations.
Myrabolans is one of the most important of the pyrogallol tanning materials.
It is particularly advantageous to blend judiciously the two main types of material, the pyrogallol and catechol tans.
Valuable pyrogalloltannins are obtained from oak wood and chestnut wood, but the woods are not used in tanning as the percentage of tan is so small.
They naturally influence the colour of leather made with catechol tans, which is usually distinctly redder than the leather made from pyrogallol tans.
Solutions of pyrogallol tans all give a blue-black colour with a dilute solution of ferric alum.
Pyrogallol tans yield no precipitate with bromine water.
Other pyrogallol tans are also used to a limited extent.
Pyrogallol tans=, which are oftenest obtained from fruit or leaves, contain usually about 52 per cent.
If a tannin infusion be largely diluted with hard water and a little iodine solution added, the pyrogallol tans yield either a purple-red or a dark blue colour, the former being a reaction of gallic acid.
If a solution of sodium arsenate be added to an infusion of pyrogallol tan diluted until no longer distinctly coloured, and the mixture allowed to stand for about two hours, a green colour develops at the surface of the liquid.
This is deposited as an insoluble yellow powder from infusions of many pyrogallol tans, by boiling with dilute acids only, allowing them to stand for a few days.
The tannins are classified into "pyrogallol tans" and "catechol tans," according to the parent phenol.
Sumach[3] is the other pyrogallol tan of commercial importance.
The chromate and iodine tests mentioned for pyrogallol tans give negative results with the catechol tans, but bromine water gives a precipitate, and sulphuric acid a crimson colour.
As a leather for bookwork when tanned with a pyrogallol tannage it is soft and kind to the touch, having few equals and no superiors.
Further, it was found in every case where authentic bindings dating from the 13th century onwards were examined the tanning material used was one of this pyrogallol series.
By degrees the required phantom image will make its appearance, and now bromide and pyrogallol are added until it is evidently complete.
After a final rinse with water the plate is treated with the pyrogallol solution and restrainer in the proportion recommended for the ordinary development of the plate, omitting the alkali.
If one wishes to exercise artistic treatment, then in the preliminary stage more importance can be given to any desired part by applying a camel's hair brush soaked in normal pyrogallol solution with its restrainer.
The plate should first of all be thoroughly soaked in a solution of the alkali which can be used, and then a few drops of the pyrogallol solution be dropped into the developing cup with an equal number of drops of the restrainer.
When this was properly out, the intensifier of silver nitrate and pyrogallol was applied, and the picture gradually brought up to printing density.
It exhibits all the characteristic properties which have been listed above for tannins in general and responds to all the characteristic reactions of a pyrogallol tannin.
These differ in their characteristic reactions as follows: Pyrogallol variety Catechol variety Ferric salts Dark blue Greenish black Bromine water No precipitate Yellow or brown precipitate Leather Produce a "bloom" No "bloom" Conc.
The process must be carried out in the order named, as the pyrogallol solution will also absorb carbon dioxide, while the cuprous chloride solution will also absorb oxygen.
Pyrogallol tannins give a blue-black coloration or precipitate with ferric salts, and catechol tannins a green-black; and whereas bromine water gives a precipitate with catechol tannins, it does not with pyrogallol tannins.
In the list of materials two have been placed in a subsidiary class because they are a mixture of catechol and pyrogallol tannin.
Pyrogallol tannins include some of the lightest coloured and best materials known, and, speaking generally, the leather produced by them is not so harsh or hard as that produced with catechol tannins.
But although pyrogallol is a benzene derivative, and could if necessary be prepared synthetically, it can hardly be claimed as a tar product, as it is generally made from gallic acid.
Pyrogallol 5 parts Water 500 parts After the development, which requires but a few moments, it suffices to wash the material to fix the image by eliminating the soluble compounds.
If a solution of pyrogallol be substituted to that of gallic acid, the tone is green, and to a green bordering to black when a solution of catechu is used, the catechu exerting at the same time a tanning action on the gelatine.
The one called the pyrogallol group, which includes sumac, gall nuts and oak bark, is commended by the Committee of the Society of Arts.
The United States Government Printing Office proposals call for leathers tanned with a pyrogallol tannin, since it has been proved that such leathers prove most resistant to the evil effects of light, heat and gas.
They were unable to obtain growth of the germ in the presence of the ordinary atmosphere, nor in the absence of oxygen (Pyrogallol method).
The pyrogallol method of Preisz also proved to be unreliable in his hands.
The pyrogallol tannins give a bluish-black colour, and the catechol tannins a greenish-black, with iron salts.
It contains 30 to 32 per cent, of tannin of the pyrogallol class, and gives a very light-coloured and almost white leather.
Generally, the best mixed tannages for solid leather consist of a combination of both pyrogalloland catechol tannins.
It is the only pyrogallol tannin which does not deposit bloom, or ellagic acid, on the leather.
Pyrogallol tannins give a light coloured, soft leather, and can be used alone satisfactorily; but heavy leathers, such as sole and belting, need a blend of both kinds of tannin.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "pyrogallol" in a variety of sentences. We hope that you will now be able to make sentences using this word.
