Peter Sterios mentions the text in a Yoga Journal article, For beginners, Balasana
In "Salutation to the Teacher and the Eternal One," a paper written by T. Krishnamacharya and distributed to students at the Yoga Mandiram in Madras, he says: "One important thing to be constantly kept in mind when doing asanas is the regulation of the breath. It should be slow, thin, long, and steady: breathing through both nostrils with a rubbing sensation at the throat and through the esophagus, inhaling when coming to the straight posture, and exhaling when bending the body."
and Shandor Remete mentions it in his book Shadow Yoga
“… During this time, I also had the good fortune to receive some of the early writings of Sri T. Krishnamarcharya of Madras. Among these, one short work has influenced me profoundly: Salutation to the Teacher and the Eternal One. It has been this book more than any other that has helped me to decipher and understand the ancient hatha yogic texts in their fullness…”
However, since receiving the text I haven't been able to confirm to what extent, if at all, it was written by Krishnamacharya. At times there seems to be a mixture of styles, was it perhaps a series of notes by Krishnamacharya for a book project that never materialised and ended up being passed around among students of KYM, who in turn added notes to the text. Or perhaps it was lecture notes written by Krishnamacharya for a course at KYM presented by someone else who then responded to questions from students.
Either way it's a fascinating document.
Here are a couple of sample pages, the full 41 page text can be downloaded from my Googledocs page.
The text continues for another forty pages and can be downloaded in full from my google docs page