A piece of the stuff to be examined is well washed with boiling water and dried, then laid in a mixture of 2 parts of dried nitrate of potash and 3 parts of ordinary sulphuric acid, and left in intimate contact with it for 8 or 10 minutes according to the strength of the labric. After a complete washing and drying, the piece of stuff which has been changed by the nitric acid is decocted with ether, to which some alcohol is added; the more consistent the collodion thus obtained, the more cotton was there in the linen. If no cotton be in it, the etherial deeoction is scarcely thickened. If it is wished to determine the quantity of cotton, it is only necessary to weigh the linen after it has been boiled with water and dried, then to proceed as above, separate the collodion obtained from the residue (which is unchanged linen), wash this well with some ether and alcohol, dry and weigh it; the loss of weight gives the quantity of cotton with tolerable accuracy.