Rice, Craig as George Sanders -- Crime on My Hands (1948)

George Sanders' Crime on My Hands (1944), ghosted by Craig Rice and Cleve Cartmill.

Full review: http://moonlight-detective.blogspot.com/2011/12/ghost-in-his-name.html

David Pringle posted the following in the comment section of the review on the Detection by Moonlight blogspot:

I haven't read the novel, which was published in 1944, but you helpfully provide us with a quotation from it, and as I read that a clue leapt out at me. This is supposed to be George Sanders, actor-detective, speaking:

"The vogue is for the light-hearted playboy with a butter heart and iridium brain to become involved in a murder situation."

The phrase "butter heart and iridium brain" is striking, isn't it? I don't know how common the expression "butter heart" was back in the 1940s, but it seems to me that the "iridium brain" is what really needs some accounting for.

Who was writing about "iridium brains" in the early 1940s?

Answer (thanks to a Google search): Isaac Asimov. As he later said...

"When I wrote my first few robot stories in 1939 and 1940, I imagined a 'positronic brain' of a spongy type of platinum-iridium alloy. It was platinum-iridium because that is a particularly inert metal and is least likely to undergo chemical changes..." < http://readr.ru/william-wu-cyborg.html#ixzz1hORzrxrJ >

Those early robot stories of Asimov's weren't collected in book form, as _I, Robot_, until 1950.

Who, in 1944, or slightly earlier, is the most likely person to have come across them in _Astounding SF_ -- George Sanders, Craig Rice ... or Cleve Cartmill?

Another interesting comment by David Pringle:

I've just re-read "The Darker Drink" (aka "Dawn") -- first published in _Thrilling Wonder Stories_, October 1947. Unlike most of Leslie Charteris's "Saint" stories, it's a light psychological fantasy about reality and illusion, and look what I found in it:

"He knew that this fat man, though butter-voiced, had a heart of iridium."

("Dawn" ["The Darker Drink"] reprinted in _Saint Errant_ by Leslie Charteris, 1948; Hodder ed., 1949, p240.)

Compare:

"The vogue is for the light-hearted playboy with a butter heart and iridium brain to become involved in a murder situation."

(_Crime on His Hands_ by George Sanders, 1944, said to have been ghosted by Cleve Cartmill.)

"The Darker Drink" may have been bylined "Leslie Charteris," but I'm sure it was ghost-written by Cartmill -- old iridium brains himself.