At the last session of the Council of Florence, Pope Eugene IV issued a Decree to the Armenians who were seeking unity with the Holy See. "We have considered it expedient, lest in future there be any hesitation among the Armenians about the truth of the Faith, and so that they might believe in all things with the Apostolic See, and that the union itself may last, stable and perpetual without any scruple ... to hand over, with the approval of this Council of Florence, the truth of the orthodox Faith in a brief compendio." In what followed, he defined the matter of Order as "the Porrection [handing by the bishop to the ordinand] of the chalice with wine and of the paten with bread".
It was common belief among medieval Latins that this ceremony was indeed the "matter", the essential ceremony, for conferring the Sacrament. It is, of course, not ancient; the Western Churches themselves lacked it during the first millennium. What is even stranger is that there were Armenians - and Greeks - at Florence, who had been ordained without this ceremony; and there was no suggestion that they should be reordained. Strangest of all, when in subsequent centuries groups of Orientals (such as the Ukrainians and the Melkites) sought unity with the Holy See, there was never any suggestion that there was any flaw in their orders, or even that they should add the Porrection of the Instruments to their rites for the future.
Did I say strangest of all? Wrongly; because even stranger was the fact that this rule, that priestly ordination is conveyed by the Porrection of the Chalice and Paten, a rule given to Orientals but then ignored both by them and by the Holy See in its dealings with them, was actually applied ruthlessly within the Western Church. In fact, it continued to be the rule in the West until the Apostolic Constitution Sacramentum Ordinis of Pope Pius XII in 1947. Let us be quite clear what this means.
In big pontifical rites of the pre-modern period, things were by no means as tidy and rehearsed as they are now. It was, apparently, possible for ordinations to happen in which some ordinands got missed out during some parts of the rite. A series of Roman decrees dealt with the question of what happened if an ordinand received the laying on of hands but missed the Porrection of the Chalice and Paten. The rule was that the ordination was invalid and must be repeated in toto and unconditionally. (It even had to be repeated conditionally if an ordinand had touched the wrong bits of the vessels, or if some clumsy fool in the sacristy had put more water than wine into the Chalice.)
Imagine yourself in London in 1946. A young man, let us imagine, at an ordination in Westminster Cathedral, by accident receives the laying-on of hands but not the Porrection of the Instruments. Across the city, an Anglican youth receives the Anglican rite of ordination, in which, at that time, the Porrection of the Instruments was not included. In the eyes of Rome, both young men equally have failed validly to receive the Sacrament of Order, the Catholic just as much as the Anglican.
It is not difficult to see why Roman praxis, from Cardinal Pole until the 1890s, routinely treated Anglican Orders as invalid.