Quote Originally Posted by jochen View Post
Sodiummetaborate-tetrahydrate (x 4 H2O) and -octahydrate (x 8 H20) are in fact the same. The formula for the first is NaBO2 x 4 H2O and for the second Na2B2O4 x 8 H2O which is the double of the first. You can see a good data sheet on the website of 20 Mule Team Borax (www.borax.com). Also on the market is the dry (sicc.) version without crystal water, but "Kodalk" was the hydrate.
This is, unfortunately incorrect, and if you do the research you will find that there is NaBO2 * 2 H2O, NaBO2 * 4 H2O, Na2B2O4 * 4 H2O and Na2B2O4 * 8 H2O

The first and the third in this list are the tetrahydrate, the second and the fourth are both the octohydrate, and tetrahydrate and octohydrate are indeed different in water content.