On Alchemy
Latin Grammar: The Gerundive
Ad quartum dicendum quod in lixivio, et in aquis sulphureorum balneorum, potest fieri Baptismus, quia tales aquae non incorporantur per artem vel naturam aliquibus corporibus mixtis, sed solum alterationem quandam recipiunt ex hoc quod transeunt per aliqua corpora.
The Gerundive
Aquinas introduces each reply to an objection with the gerundive dicendum. The gerundive is a verbal adjective. When it is applied to a noun, it expresses obligation or necessity.
The gerundive can also be used with the verb esse to express necessity — this is what Aquinas is doing (although the est must be supplied by the reader). This forms the passive periphrastic and it is always translated as a passive (i.e. dicendum est: "it must be said").
Make the following Latin sentences express obligation. Change the main verb into the passive periphrastic construction using the gerundive. Remember that the gerundive is formed by adding -ndus, -nda, -ndum to the present stem and it must agree in gender, number, and case with the noun that is modifies.