OK, if you have to ask, there are several reasons, but first and foremost, many of the substances used in these recipes are now known to be extremely toxic. For example, many of the formulas given call for the use of mercury or lead, or one of their compounds, and many of the recipes they are used in here could present serious health hazards. It is just not worth the risk.
Second, some of the reagents called for may still be available, but the names used in Henley's are now archaic. In some cases, it is possible to identify the modern name for the reagent by using a search engine to at least some degree of accuracy, but even with some of these reagents, you had better be sure you are using exactly what the author had in mind.
Many other ingredients called for are no longer available, having long since been replaced by better synthetic materials. Items such as gutta-percha, isinglass, or gum Arabic are a little tough to find nowadays. In addition, many herbs are listed that were once part and parcel of the corner drugstore, but they, too, have been replaced.
Some of the reagents or substances that are still available are very dangerous in inexperienced hands, such as concentrated hydrochloric and sulfuric acids. This is also true of mercury and its compounds, as well as lead compounds. Also, concentrations of some solutions are based on the Baumé system which is no longer used. Converting these concentrations is possible, but it would require some effort.
Our understanding of
chemistry has advanced considerably in the last century,
and much of the information regarding atomic weights,
etc., is simply outdated. Best to use this as a
glimpse into the way things were done several
generations ago, and to reflect on how far we have
Finally, the web version was created by comparing the scanned PDF obtained from the Internet Archive with the text version generated by OCR software. There were numerous errors in the generated OCR text, and while every effort was made to weed out the errors, we are confident that not every error has been found! Some have probably crept in from the conversion to HTML as well.
And if those are not enough good reasons, understand that even when this book was first published, a common complaint was that some of the recipes included in collections such as this did not always work. So for all of the above reasons, we once again offer the following...
DISCLAIMER: There are a many good reasons not to try to reproduce any of the formulas today (see above), and The Science Notebook assumes no responsibility whatsoever if you decide not to heed this caution. You have been warned!