Though titled etymology, the text is not about the origin of the name of the city, but in fact King Mongkut complains about the inconsistent and varying spellings of the name in western source.
But as the city P'etch'ără-booree the masses of the people in all parts call it P'ripp'ree or P'et-pree. The name P'etch'ără-booree is Sanskrit, a royal name given to the place the same as T'on-booree, Non-booree, Năk'awn K'u'n k'ăn, Sămŏŏtă-pra-kan, and Ch'ă-chong-sow. Now if Mahá nak'awn be called Bangkok, and the other names respectively called Tălát-k'wan, Paklat, Paknam, and Păătrew, it is proper that P'etch'ără-booree should follow suit, and be called by her vulgar name P'rip-p'ree, or P'et-p'ree.
Now that the company of teachers and printers should coin a name purporting to be after the royal style and yet do not take the true Sanskrit, seems not at all proper. In trying to Romanize the name P'etch'ără-booree, they place the mark over the a thus P'etchă-booree, making foreigners read it P'etcha-booree, following the utterances of old dances in the temples, who boast that they know Balăm Bali, and not satisfied with that, they even call the place City P'et, setting fortn both the Bali and the meaning of the word; and thus boasting greatly of their knowledge and of being a standard of orthography for the name of that city.
Now what is the necessity of coining another name like this? There is no occasion for it. When the name is thus incorrectly printed, persons truly acquainted with Sanskrit and Bali (for such there are many other places) will say that those who write or print the name in the way, must be pupils of ignorant teachers - blind teachers not following the real Sanskrit in full, taking only the utterances of woodsmen, and holding them forth [as the correct way.] In following such sounds they cannot be in accord with the Sanskrit, and they conclude that the name is Siamese. Whereas, in truth, it is not Siamese. The true Siamese name is P'rip-p'ree or P'et-p'ree. It matters not what letters are used to express it - follow your own mind; but let the sound come out clear and accurate either P'rip-p'ree or P'et-p'ree, and it will be true Siamese. But the mode of writing and printing the name P'etchă-booree with the letter a and mark over it and other marks in two places, resists the eye and the mouth greatly. Whatever be done in this matter let there be uniformity. If it be determined to follow the vulgar mode of calling the name, let that be followed out fully and accurately; but if the royal mode be preferred, let the king be sought unto for the proper way of writing it, which shall be in full accordance with the Sanskrit. And should this happen not to be like the utterance of the people in the temples the difference cannot be great. And persons unacquainted with Sanskrit will be constrained to acknowledge that you do really know Sanskrit; and comparing the corrected with the improper mode of Romanizing, will praise you for the improvement which you have made. Such persons there are a few, not ignorant and blind leaders and dunces like the inmates of the temples and of the jungles and forests, but learned in the Sanskrit and residents in Siam.