Rachael,

You will find a fair bit of biographical information about Alfred if you use google.com.br and cut&paste what you find into Google Translate (I'm assuming you're not fluent in Portuguese!).

The Alfred Slater building still exists at the Mackenzie Institute.

Alfred died in 1958, two years before John Henry.

Regards,
Jon
(my connection is via the Newcastle Slaters, of whom Alfred's father John George was a scion).