DYEING AND CALICO PRINTING.

296

It would be interesting to re-examine this substance with the improvedmeans of chemical analysis now at command. To the list of the salts quotedby M. Perrot must be added alkaline phosphates, which, to some extent, existin all animal excrements. M. Perrot also observed that the soluble portion ofthe cow-dung yields in the cold an abundant precipitate with the red liquor,which increases when the fluid is heated. The insoluble portion of the dungretains, on being boiled with red liquor, a certain proportion of alumina.M. C. Koechlin has made some experiments with the contents of a dung-bathmade up in the usual manner, and therefore containing 80 kilos, dung, withfrom 40 to 45 measures of water, temperature 70°, after there had beenpassed through it several pieces of cloth, mordanted for good black, fine red,and purple. The bath was not at all exhausted : on being left quietly standingthe liquid did not become clear; there remained in suspension a black greenish-coloured matter, weighing 9 5 grms. for 25 litres of the liquid operated upon.The filtrate had a dirty yellow colour, was astringent, and so acid as to colourblue litmus-paper red. Normal dung is either quite neutral or alkaline. Onbeing evaporated to dryness the liquid left 22'8 grms. residue. The previouslysuspended ligneous matter retained on the filter weighed, after, drying, about28 grms. The incineration of these various substances yielded, on analysis,the following quantities of alumina and peroxide of iron :—

Ligneous matter.j Alumina .. ..

1 Peroxide of iron

Suspended matter (9-5 grms.)! Alumina

1 Peroxide of iron

Soluble matter (22-08 grms.) I ^ um ' na • •

l Peroxide of iron

It should be observed that the relatively small proportion of alumina containedin the aqueous extract could not be detected by any of the usual reagents,being consequently masked by the presence of organic matters. Add to thisthe faCt that the aqueous extract of a dung-bath, after it has been used for theclearing of mordanted goods, contains invariably almost as much alumina.asthe insoluble portion, yet white calico is not mordanted on being immersedin this liquid, thus proving that the alumina is in an unusual condition. Thesame applies to the iron mordants. When to a freshly-made aqueous infusionof cow-dung gradually increased quantities of the acetates of iron and ofalumina are added, it will be seen that the precipitation does not ensue imme-diately, but only appears when a certain limit is reached. There is thus goodreason to suppose that cow-dung contains a soluble substance, probably of analbuminous nature, which possesses the property of preventing the precipita-tion of the alumina and oxide of iron by the usual reagents.

According to these results the influence of cow-dung in cleansing may beviewed in the following manner :—The first portions of the acetates of aluminaand iron which are separated from the goods remain in solution, but cannotinjure the white portions of the fabric, and this continues as long as themasking power of the organic compounds is not exhausted. At the momentof that exhaustion taking place a precipitation of the oxides ensues, in con-sequence of the atftion of the alkaline phosphates, and when at last this usefuleffeCt is also at an end all the portions of the mordant which become detachedcan attach themselves to the white portions of the goods. It is therefore

o’i86 grm.0-021 „

0-665 >.

°’456 „

o'66o ,,o-ooo „