My local library has a copy of the tenth edition of Samuelson's Economics, from 1976 (with assistance from Peter Temin). In an early chapter, Samuelson distances himself from the notion that interest is a reward to a contribution to production, while not exactly denying this idea:
"Part Four will show that, just as wages and rent are the factor-prices of primary labor and land, the 4 or 6 or 10 per cent interest rate per annum can, in a more subtle way, be regarded by the apologists for capitalism, as the factor-price that rations and rewards society's scarce supply of various capital goods and investment projects." (Chap. 3)Part 4 begins with the statement that the theory of distribution is controversial:
"The theory of distribution is still in an unsettled state." (Chap. 27)Samuelson says the issue is how much of distribution can be explained by market forces and how much by power.
In Chapter 27, Samuelson explains distribution with a model with labor and land. He later introduces capital goods and argues that, in equilibrium, the marginal product of capital is equal to the "price charged for use of capital good." This is distinguished from the interest rate. Chapter 27 also presents the "aggregate american production function."
Chapter 30 is more explicitly about capital. Samuelson talks about "roundabout processes." Samuelson also says:
"At this point we can greatly simplify the exposition of the traditional theory if we agree to concentrate on the case where all physical capital goods are exactly alike and highly versatile." (Chap. 30)An appendix to Chapter 30 has a section titled, "Reswitching and all that", with a footnote:
"This section may be skipped. Footnote 5's fine point provided an example of reswitching for a durable machine."
I don't recall that I found all these distinctions when dipping into later editions. As I recall, Samuelson deleted that appendix and all mentions of reswitching. He had firms "usually" adopting more capital-intensive techniques at lower rates of interest. I read that qualification as referring to the Cambridge Capital Controversy, but did not see how students could get that. They might read Samuelson as merely acknowledging the possibility of entrepenuers making mistakes.