Excerpt from Journal of the Franklin Institute of the State of Pennsylvania, Vol. 4: Devoted to the Mechanic Arts, Manufactures, General Science, and the Recording of American and Other Patented Inventions

From the time when it was known that the acetate of alumine was preferable, as a mordant, to alum, it was admitted, as a necessary consequence of this discovery, that the best proportions for obtaining the acetate, were precisely those in which the two salts were most completely decomposed. And chemical analysis has shown that 100 parts of alum contain 10.5, or nearly, of alumine, but 10.5 of alumine require for their saturation 31.5 of acid: and it will take no less than 116 parts of acetate of lead to furnish this quantity of acetic acid.

We know that the common alum is composed of sulphuric acid, alumine, potash, and water, and we may also consider it as being composed of sulphate of alumine, sulphate of potash, and water. We also know from experiment, that if a certain portion of the acetate of lead be first added, it will become united by preference with the sulphate of alumine, and the only aim of this process being to obtain the acetate of alumine, it results that it is useless to employ more of the acetate of lead than is sufficient to decompose the sulphate of alumine, as all which we add above that proportion is entirely lost.

Agreeably to the data we have given, we admit that the most convenient proportions to obtain a completely reciprocal decomposition, are, 100 parts of alum to 116 of the acetate of lead, supposing that these two salts are in a state of purity, and do not contain more than their proper proportion of water.

As to the mode of preparing this mordant, that possesses no difficulty, only, that as the alum is but little soluble in cold water, so it is convenient to make the solution by heat, and in four parts or more of water. After the solution is effected, we add a little sub-carbonate of soda to saturate the excess of acid before we add the acetate of lead, this may be about a tenth part of the weight of the alum: and we then add the proportion of acetate of lead, well powdered and sifted, we then briskly stir the mixture, and renew the stirring from time to time, until it is become quite cold. We then allow it to remain at rest to deposit, and draw it off by the help of a syphon, lastly, we throw the sediment upon a filtering cloth, and strain it hard, in order to obtain the last portions of the liquid.

The mordant thus composed, is one of the strongest which can be employed, and it is seldom necessary to concentrate it, but rather to employ water to dilute it to the requisite degree, and we also know that when thus diluted, it keeps the better.

Most manufacturers, instead of pursuing the course we have indicated, prefer to employ less acetate of lead in procuring the weaker mordants, and think that they find an economy in doing so.

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