estigation and research--the
bearing of Chemistry upon Physiology, Medicine, and Agriculture,--which
may be said to be only just begun.

My friend, Dr. Ernest Dieffenbach, one of my first pupils, who is
well acquainted with all the branches of Chemistry, Physics, Natural
History, and Medicine, suggested to me that a collection of these
Letters would be acceptable to the English public, which has so
favourably received my former works.

I readily acquiesced in the publication of an English edition, and
undertook to write a few additional Letters, which should embrace
some conclusions I have arrived at, in my recent investigations, in
connection with the application of chemical science to the
physiology of plants and agriculture.

My esteemed friend, Dr. Gardner, has had the kindness to revise the
manuscript and the proof sheets for publication, for which I cannot
refrain expressing my best thanks.

It only remains for me to add a hope, that this little offering may
serve to make new friends to our beautiful and useful science, and
be a remembrancer to those old friends who have, for many years
past, taken a lively interest in all my labours.

JUSTUS LIEBIG

Giessen, Aug. 1843.

CONTENTS

LETTER I

The Subject proposed. Materials employed for Chemical Apparatus:--
GLASS--CAOUTCHOUC--CORK--PLATINUM. THE BALANCE. The "Elements" of
the Ancients, represent the forms of matter. Lavoisier and his
successors. Study of the materials composing the Earth. Synthetic
production of Minerals--LAPIS LAZULI. Organic Chemistry.

LETTER II

Changes of Form which every kind of Matter undergoes. Conversion of
Gases into Liquids and Solids. Carbonic Acid--its curious properties
in a solid state. Condensation of Gases by porous bodies. By Spongy
Platinum. Importance of this property in Nature.

LETTER III

The Manufacture of Soda from Culinary Salt; its importance in the
Arts and in Commerce. Glass--Soap--Sulphuric Acid. Silver Refining.
Bleaching. TRADE IN SULPHUR.

LETTER IV

Connection of Theory with Practice. Employment of MAGNETISM as a
moving power--its impracticability. Relation of Coals and Zinc as
economic sources of Force. Manufacture of Beet-root Sugar--its
impolicy. Gas for illumination.

LETTER V

ISOMERISM, or identity of composition in bodies with different
chemical and physical properties. CRYSTALLISATION. AMORPHISM.
ISOMORPHISM, or similarity of properties in bodies totally d