“The slaves of developed industrial civilization are sublimated slaves.”

As quoted in His Brother's Blood: Speeches and Writings, 1838–64 https://books.google.com/books?id=qMEv8DNXVbIC&pg=PA193&lpg=PA198 (2004), edited by William Frederick Moore and Jane Ann Moore, p. 198
1860s, Speech to the U.S. House of Representatives (April 1860)

in P. Beresford Ellis (ed.), James Connolly - Selected Writings, p. 191.

Source: Little Essays of Love and Virtue http://www.gutenberg.org/files/15687/15687-h/15687-h.htm (1922), Ch. 7

Platform of the Free Soil National Convention (1848).

The Minister's Wooing (1859) Ch. 1 Pre-Railroad Times.
Context: He was called a good fellow, — only a little lumpish, — and as he was brave and faithful, he rose in time to be a shipmaster. But when came the business of making money, the aptitude for accumulating, George found himself distanced by many a one with not half his general powers. What shall a man do with a sublime tier of moral faculties, when the most profitable business out of his port is the slave-trade? So it was in Newport in those days. George's first voyage was on a slaver, and he wished himself dead many a time before it was over, — and ever after would talk like a man beside himself, if the subject was named. He declared that the gold made in it was distilled from human blood, from mothers' tears, from the agonies and dying groans of gasping, suffocating men and women, and that it would sear and blister the soul of him that touched it; in short, he talked as whole-souled, unpractical fellows are apt to talk about what respectable people sometimes do. Nobody had ever instructed him that a slaveship, with a procession of expectant sharks in its wake, is a missionary institution, by which closely. packed heathens are brought over to enjoy the light of the Gospel. So, though George was acknowledged to be a good fellow, and honest as the noon-mark on the kitchen floor, he let slip so many chances of making money as seriously to compromise his reputation among thriving folks. He was wastefully generous — insisted on treating every poor dog that came in his way, in any foreign port, as a brother — absolutely refused to be party in cheating or deceiving the heathen on any shore, or in skin of any color — and also took pains, as far as in him lay, to spoil any bargains which any of his subordinates founded on the ignorance or weakness of his fellow-men. So he made voyage after voyage, and gained only his wages and the reputation among his employers of an incorruptibly honest fellow.

For what price, tell me? What did you find in existence worth as much as this human nature? What price did you put on rationality? How many obols did you reckon the equivalent of the likeness of God? How many staters did you get for selling that being shaped by God? God said, Let us make man in our own image and likeness. If he is in the likeness of God, and rules the whole earth, and has been granted authority over everything on earth from God, who is his buyer, tell me? Who is his seller? To God alone belongs this power; or, rather, not even to God himself. For his gracious gifts, it says, are irrevocable. God would not therefore reduce the human race to slavery, since he himself, when we had been enslaved to sin, spontaneously recalled us to freedom. But if God does not enslave what is free, who is he that sets his own power above God's?
Homilies on Ecclesiastes; Hall and Moriarty, trs., de Gruyter (New York, 1993) p. 74 https://books.google.com/books?id=BReXJwwE_D8C&pg=PA74&lpg=PA74.

A Human Being Cannot Be Justly Owned (1835)
Context: The slave-holder claims the slave as his Property. The very idea of a slave is, that he belongs to another, that he is bound to live and labor for another, to be another’s instrument, and to make another’s will his habitual law, however adverse to his own. Another owns him, and, of course, has a right to his time and strength, a right to the fruits of his labor, a right to task him without his consent, and to determine the kind and duration of his toil, a right to confine him to any bounds, a right to extort the required work by stripes, a right, in a word, to use him as a tool, without contract, against his will, and in denial of his right to dispose of himself, or to use his power for his own good. “A slave,” says the Louisiana code, “is in the power of the master to whom he belongs. The master may sell him, dispose of his person, his industry, his labor; he can do nothing, possess nothing, nor acquire any thing, but which must belong to his master.” “Slaves shall be deemed, taken, reputed, and adjudged,” say the South-Carolina laws, “to be chattels personal in the hands of their masters, and possessions to all intents and purposes whatsoever.” Such is slavery, a claim to man as property. Now this claim of property in a human being is altogether false, groundless. No such right of man in man can exist. A human being cannot be justly owned. To hold and treat him as property is to inflict a great wrong, to incur the guilt of oppression.

Arrian, Anabasis Alexandri, Book VII : Indica, as translated by Edgar Iliff Robson (1929), p. 335

2000s, The Real Abraham Lincoln: A Debate (2002), The South was a Closed Society
Context: There were eight of them that had laws trying to protect black people who were free from being kidnapped as slaves, because under the law of 1850, the Fugitive Slave Act. If a Southerner came across from Virginia to Pennsylvania and saw a black man that he thought he would like to have as a slave, he had to say, 'Well, that’s my runaway slave', and this runaway slave would then be arrested and confined, and then there would be a hearing before a federal commissioner. And the would-be slave owner could summon witnesses—as many as he wanted. The man accused of being a slave could summon no witnesses, had no counsel. And if the federal commissioner decided he was a slave, he was paid $10, and if he decided he was a free man, he was paid $5. It’s hard to imagine any law passed in either Nazi Germany or Stalin's Russia that was more inconsistent with the principles of civil liberty than the Fugitive Slave Act.