This is a book that is used to store all of your MineChem recipes. You can store recipes in your chemist's journal by placing your book into a Microscope and placing an object underneath the Microscope, this will add the object and the elements it contains into your chemist's journal. You can also store recipes in your chemist's journal by placing it in a Chemical Synthesis Machine, and creating something will store what you created in your Chemist's Journal.
On the left is a picture of what a Chemist's Journal looks like when it is used. If you click on any of the objects that are stored in your journal, you can find out what elements are used to create that object or compound in a Chemical Synthesis Machine (and the power required to create this object in MJ). The journal will also tell you what elements that object or compound will give you if it is placed in a Chemical Decomposer (and the percent chance of getting the listed chemicals from that object or compound).
The Chemist's Journal is crafted by placing one book and one Empty Vial in the crafting grid, this recipe is shapeless.