Potter's Sulphide Ore Treatment Ltd v Sulphide Corporation Ltd

This case involved an appeal to the High Court of Australia from a decision of the Supreme Court of New South Wales concerning interrogatories in a patent infringement suit. The parties were Potter's Sulphide Ore Treatment Ltd. (the plaintiffs and appellants) and Sulphide Corporation Ltd. (the defendants and respondents). The dispute centred on the plaintiffs' allegation that the defendants were infringing their patent for an improved process for separating metallic sulphides from sulphide ores, either by using the patented process directly or a colourably different one.

The legal issues before the High Court were whether the plaintiffs were entitled to administer certain interrogatories to the defendants regarding their process for treating sulphide ores, and whether the Supreme Court had erred in limiting the scope of these interrogatories. Specifically, the court had to determine if the plaintiffs could interrogate the defendants about the proportions of acid used in their process and the detailed particulars of their process, even if those details might not directly prove infringement but could contribute to establishing the plaintiffs' case or undermining the defence.

The High Court reasoned that any facts relevant to the matter in issue could be the subject of interrogatories, regardless of who bore the burden of proof. The court found that the questions regarding the proportion and percentage of acid used by the defendants were material because the plaintiffs' case relied on demonstrating that the defendants were using the patented process in substance, even if they substituted mechanical or chemical equivalents for parts of it. The court also held that the plaintiffs were entitled to ask the defendants to describe the particulars in which their process differed from the plaintiffs' specification, as this was a relevant fact within the defendants' knowledge. The court considered that the Supreme Court had unduly restricted the scope of permissible interrogatories.

Consequently, the High Court varied the order of the Supreme Court. It allowed the second paragraph of the first interrogatory as proposed by the plaintiffs, amended the third paragraph of the first interrogatory to ask for the particulars of difference from the plaintiffs' process, and allowed the tenth interrogatory as proposed. The court also agreed to adjourn the application concerning interrogatories numbered 11 to 19, as had been agreed in the court below.