Complex sentence: All of the buildings were outfitted with costly machinery, much of which had been designed and built by the firm for their special use and all tools and appliances used in the manufacture of their various articles were considered the very best.
Split into simpler sentences: All of the buildings were outfitted with costly machinery, much of which had been designed and built by the firm for their special use. All tools and appliances used in the manufactory were considered the very best.