The author's preface
"Such are the advantages offered by the Italian language that it is unquestionably advisable to learn to sing in this idiom first, after which it will be easy to sing in the other languages. Learning to sing in another language does not offer these benefits.
I have come across many people in my experience in Germany, France, England, and Italy who, desiring simply to learn to sing for their own pleasure, are unwilling to embark on long exercises and solfèges, and as a result, their study lacks any method.
I therefore decided to prepare a new and entirely new method, which might prove both useful and enjoyable and while avoiding the boredom of long studies would achieve the same end.
Since the principal difficulty for foreigners (even after doing vocalizes and solfèges) lies in singing a language which is not their own, I thought that it was a good idea that they should get used to the language right from the beginning of their studies. Rather than have them sing meaningless syllables I chose the most suitable of Metastasio's splendid poems as a means of inculcating those basic rules which most students neglect because they find them boring. There is no doubt that this method will prove useful not only to amateurs, but also to those who wish to make this Art their profession. It may well help to clarify points made in other methods, thanks to the use of examples."
Nicolo Vaccaj
Vocal range
"Throughout the method I have made use of a limited extension which should prove comfortable for most voices. Moreover it is always a good idea to start by practising in the centre of the voice. Indeed all the rules can be learnt in this part of the voice, and if one should so desire, any of the lessons can be transposed a tone higher or lower at will."
Source
Vaccai, Nicola; Metodo pratico di canto. Practical vocal method: contralto or bass /
Vaccaj; revisione critico-tecnica di Elio Battaglia; critical and technical revision by Elio Battaglia. Milano : Ricordi, cop. 1990.