PREFACE.

For over fifty years the Scientific American has given its readers the experiences of practical experimenters in every branch of the useful arts. The formulas have been largely garnered from the columns of "Notes and Queries" and "Correspondence," which have for many years been widely read on account of their variety and value. This source of useful information, widely scattered and unclassified, has now been carefully brought together, digested and condensed. In addition, laborious researches have been made among the difficult and inaccessible mysteries known as "trade secrets." Many kindred works have been consulted, such as Cooley, Spon, etc., and acknowledgments are due for any formulas obtained from these sources. The success of this compilation is shown by the fact that in nine years twelve large editions have been issued. The publishers have now thought it desirable to bring out a revised edition in which the latest formulas could be given, as the changes in the last ten years, particularly in the line of such s jects as photography, have been very marked, and the Editor has been guided in this selection by thousands of letters from those who have used the book in its earlier editions.

A few hints as to the use of the work will not, perhaps, be out of place. It should be remembered that the working of a formula requires considerable skill, and it cannot be expected that the beginner can make articles at first which will compare with those on the market. The use of wrong raw materials is a fruitful source of trouble, and it should be remembered that a large number of articles called for in formulas cannot be obtained at the druggist's, although such materials can usually be purchased at wholesale chemical establishments in large cities. The use of impure materials, or materials which have deteriorated, is also a frequent source of error.

92024